Friday, October 25, 2013

Sweet potato harvest

Ajay Nair
Department of Horticulture
Iowa State University

Our sweet potato harvest took place on October 17th, 2013, three weeks later than 2012. Overall the crop grew well. Slips were planted on June 7, 2013 on black plastic mulch. The mulch helps increase soil temperature and suppress weeds. Weeding was minimal, only two times, until the canopy closure. The crop was affected by Japanese beetles but the plants came out of it gradually.

The harvest team
It is picking time !

The undercutter; used to lift potatoes
Undercutter in action

We conducted two experiments this year, one identifying suitable cultivars for Iowa growing conditions and the other investigating appropriate spacing of sweet potatoes. Data will be soon analyzed and made available through ISU Research Farm Progress Reports and at

Wednesday, October 2, 2013

Cover crop status

Dr. Ajay Nair
Department of Horticulture
Iowa State University

We seeded our cover crops during on 09-05-2013 for 2014 field study that will focus on the use of cover crops and conservation tillage practices in vegetable production systems. The plot is located at the Horticulture research Station, Ames, IA. So far cover crops are doing great. Pictures below were taken on 09-26-2013.

This was the second seeding of cover crops as the first seeding was not uniform. We decided to tear the plot and seed again. Both times Tye Pasture Pleaser seeder was used. The reason for the non-uniform germination of the first seeding was attributed to seeding depth. Cereal rye is sensitive to seeding depth. Although we had set the seeding depth between 1 to 1-1/4 inch, close examination of showed that the majority of seeds were at 1-3/4 to 2 inch deep. One would assume the rye to germinate and emerge at that seeding depth, but it is debatable. In our experience, the second seeding, in which rye was seeded at 3/4 to 1 inch depth, germination was excellent and the emergence was uniform (see pictures above).

Growers should monitor the seeding depth carefully as it could significantly affect emergence of cover crops. Small seeded cover crops like clovers and mustard should be handled even more carefully. 

Sunday, June 23, 2013

Cover Crop Workshop/Field day

Dr. Ajay Nair
Department of Horticulture
Iowa State University

Ames, Iowa – The sustainable vegetable production lab in collaboration with researchers at Iowa State University, USDA-National Laboratory for Agriculture and Environment and USDA-SARE are teaming up to offer three cover crop workshops this Fall at following locations:

September 27 (Friday) – Armstrong Research Station, Lewis, IA
October 4 (Friday) – Horticulture Research Station, Ames, IA
October 11 (Friday) – Muscatine Island Research Station, Fruitland, IA

Funding for these workshops is provided by USDA-SARE Professional Development Grant Program. Workshops are geared towards commercial horticulture field extension specialists, county extension horticulturists, regional food systems working group members, local food organizations, IFVGA & PFI board members, and IDALS & NRCS personnel. Fruit and vegetable growers interested in learning about cover crops are also welcome. This workshop is co-sponsored by The Leopold Center for Sustainable Agriculture.

Participants attending the workshop will learn about cover crop types, planting, management, benefits, and issues associated with cover cropping in fruit and vegetable cropping systems.  Depending on weather, there will be an opportunity to assess cover crops under field conditions. Live cover crop plants will also be on display inside.  

Registration is free but required for arranging food. Please contact Dr. Ajay Nair (; 515-294-7080).

The tentative agenda for the workshop is given below:

9:30am – 9:45
Registration and refreshments
9:45am – 10:00
Welcome, Dr. Ajay Nair, Department of Horticulture, ISU
10am - 10:45
Benefits of cover crops in crop production systems
Dr. Tom Kaspar, USDA-NLAE
10:45 - 11:30
  Envisioning a cropping systems approach
  Dr. Andy Lenssen, Agronomy, ISU
11:30 - 1:30
Lunch and field visit
1:30 - 2:15
Integrating cover crops in fruit production systems – Dr. Gail Nonnecke, ISU
2:15 - 3:00
Cover crop options for vegetable growers – Dr. Ajay Nair, ISU
3:00- 3:15 pm
Discussion, Evaluation, Adjourn

Wednesday, June 19, 2013

Potato Blackleg

Ajay Nair
Department of Horticulture
Iowa State University

Recently a number of growers had called in and also sent samples of their potato plants. The main symptom mentioned was the development of a mushy, black, soft lesion on the stem at the ground level (see pictures below). These symptoms are caused by bacterium called Erwinia carotovora and can take many forms (blackleg, aerial stem rot, or tuber soft rot). Bacteria either enter the seed potatoes and lower stems through wounds and injuries, or move directly from contaminated seed pieces to lower stems.  
Blackleg infection
Stem collapse

Affected foliage

Abundant moisture at the surface of the wounded tissue is needed for infection and continued high humidity after infection favors spread of the disease in the plant. This year's wet spring weather is conducive for the spread of this disease. The decay of seed pieces in the soil by fungi and other organisms may also provide conditions for blackleg disease to develop.

The blackleg bacterium survives poorly in soil. All evidence suggests that the blackleg bacterium does not survive very well outside of association with host plant tissue. Hence, the seed tuber is the most important source of inoculum in the blackleg disease cycle. Removal of blackleg affected plants including below-ground portions is the best option. Take steps to prevent contact of diseased tissue with other plants in the field. It is unfortunate that there is no effective chemical control to manage this disease. The first and the most effective line of defense is the use pathogen-free tubers for seed. Warming of seed tubers to about 55°F before planting also helps. Seed treatment with fungicides do not directly affect these bacterial pathogens, but fungicides can reduce invasion by other fungi and therefore reduce opportunistic infection by Erwinia spp.

Monday, May 27, 2013

A wet Spring

Ajay Nair
Department of Horticulture
Iowa State University

This past week I time traveled to my nursery days and the song which I wanted to sing badly was "Rain rain go away...Come again another day, Little Johnny wants to play". Things have been fairly wet this spring. The ground is saturated and it is hard to get in the field and plant. We need the rain but it is the timing that is causing  issues. It rains and the ground starts to dry in 3-4 days but then it rains again. As compared to last year we are late in our plantings. Last Tuesday we flail mowed our cover crops (cereal rye) and gave a shallow till to dry the soil faster. We waited for three days and last Friday when we got a small window, we went full throttle and banded fertilizer and laid plastic. Banding fertilizer in the area where the plastic is laid has several advantages:
1. Less fertilizer is used
2. Fertilizer not available to weeds that grow in the alley-way between raised beds
3. Promotes sustainability by reducing fertilizer usage

Above: Cover crops being flail mowed
Below: Plastic mulch layer in action
It is unfortunate that the rain is disrupting and delaying planting, but vegetable growers should take utmost care before deciding to run any machinery in their fields. One of the concerns is soil compaction. Under wet conditions, the effect of soil compaction could go as deep as 2 feet, depending upon the axle load of the tractor.  Heavily compacted soils contain few large pores and have reduced rate of water infiltration and drainage in the compacted layers. This can can increase runoff, thus increasing soil and water losses. Compaction directly limits root growth of crops and has the potential to reduce crop growth and yield. This year it might a little tight to find the perfect soil moisture or field condition to lay plastic mulches, all we can do is be prepared and ready to get in to the field as soon as there is an appropriate rain-less window. Meanwhile, on a lighter note, I will continue with my nursery rhyme.....Rain Rain go away....come again another day......
Normal and compacted soil

Monday, May 20, 2013

Planting time musing

Ajay Nair
Department of Horticulture
Iowa State University

Weather is fascinating. It surprises you in many ways. After months of conversation about not having moisture in the ground and a slow recovery from drought, here we are, talking about too much water in the ground! The level of anxiety among fruit and vegetable producers is on the rise. We at the Horticulture Research Station are on the same page. Every time one waits for a sweet 2-3 window to till the soil and roll the plastic mulch layer, a thunderstorm rolls in with 1-2 inches of water!

Things are a little different at the eastern end of the state, thanks to the well-drained sandy soils. It rains but you can be in the field the next day. But they have their own woes with lower organic matter and water holding capacity soils. At the Muscatine Island Research Station, Fruitland, IA  our sweet corn is 2-3 inches tall and the potatoes have sprouted and getting ready to come up the soil. We installed lysimeters in our potato sweet corn biochar study on 05-08-2013 to collect water leaching out of those soils. It will be an interesting finding to know how much of nitrates are being tied up by the biochar. A large number of high tunnel growers would be happy that this intermittent rainfall is not creating problems with their planting schedules. Most high tunnel growers have planted their crop and are looking forward to a good growing year. Our tomato plastic mulch study at the Armstrong Research Station, Atlantic, IA got planted 05-10-2013.
    Sweet corn at Muscatine
Lysimeter installed
Plastic mulch study at Armstrong Research  Station
Our lab was all excited for today (05-20-2013) to start laying our plastic mulch but the rain last night played a spoilsport. Oh well, there are things to get done in the lab. So here we are, waiting 2-3 days for that perfect level of soil moisture where the plastic mulch is laid down to perfection (straight, tight, and with good soil contact). 

Friday, March 29, 2013

It is Transplant time !

Ajay Nair
Department of Horticulture 
Iowa State University

Transplant production plays a key role in determining a successful vegetable production system. Growing good plants requires skill, proper care, and knowledge of the fundamentals of crop production. With adequate greenhouse sanitation measures, good quality seed and growing medium, greenhouse environmental conditions such as light, temperature and relative humidity, proper irrigation and fertilization, and pest and disease monitoring and management, growers can produce high quality transplants that contribute towards higher yields and productivity.

Why grow transplants?
Benefits of using transplants are many: early start, uniform growth, healthy root system, and generally free from pest and diseases. One of the major advantages is that the grower has a better control over growing conditions so that the plants are ready when needed, eliminating problems associated with unavailability of transplants during high market demand, importing of diseases with purchased transplants, and planting delays due to inclement weather conditions. Vegetable transplants provide a head-start to target early-season market, insure a good stand of vegetable plants without the uncertainty of direct seeding or the added cost of field thinning, especially with the ongoing high cost of hybrid seeds, and earlier fruit maturity than direct seeded plants.

Greenhouse sanitation
The first and the foremost thing is to prepare the greenhouse for transplant production. Practice good sanitation. Transplant production greenhouses should be free of plant debris, accumulated soils, and weeds which may harbor insect pests and diseases. Greenhouse benches, floors, should be properly disinfested prior to use. Products such as chlorine bleach, Green-Shield, Physan 20, Oxidate (hydrogen dioxide, BioSafe Systems), chlorine dioxide, etc. could be used to clean and sterilize greenhouse benches. Product labels need to be followed precisely depending upon purpose and mode of use. Disinfecting  benches and floors is an effective method to prevent disease causing organisms such as Pythium and Rhizoctonia. Sanitation is also applicable to personnel entering and handling plants in the greenhouse. This will help eliminate spread of pest and diseases due to human contamination (dirty hands, handling plants after smoking tobacco, and soil and dirt carried in shoes).

 Ventilation and heating
Greenhouses should ensure proper ventilation, air flow, and heating for healthy plant growth. Good ventilation and air circulation is important as it helps keep the foliage dry and mitigate various bacterial and fungal diseases. Well aerated and ventilated greenhouse can maintain low relative humidity thereby eliminating common diseases such as botrytis gray mold and late blight. Growers should make sure that there heaters and furnaces are properly working and maintaining desired air temperatures. Uniform temperatures are essential for adequate control of plant development and production of uniformly sized transplants. Thermometers should be placed at plant level in several locations to monitor air temperature. Temperature control is critical and should be tailored based on crop requirement. Most plant species grow very little at temperatures less than 45 to 50 degrees F (warm season vegetables like solanaceous crops) while cool season vegetables like lettuce, spinach, cabbage, broccoli, etc will grow under temperatures not suitable for warm season vegetables.

Flats and plugs
Multi-cell plastic trays are widely in use for transplant production. These trays are available in wide range of cell sizes. Cell sizes could range anywhere from 50-800. Selection of tray size depends upon plant species, duration of transplant growth, and available greenhouse space. Larger cell sizes can be used for transplants that need longer growth cycle (>5 weeks) and have larger root system like asparagus. Larger cell sizes have the advantage of holding more media, thus moisture and nutrients, but compromise on greenhouse space. For smaller cycle crops such as leafy greens a smaller cell is appropriate as the root growth seldom fills the cell space. Most growers reuse transplant trays and containers for economic and environmental reasons. Trays and containers should be sanitized with sanitizing solutions after each use to prevent the spread of diseases. Cell sizes also have an impact on spread of diseases, as closely packed cells increase relative humidity and create conducive environment for bacterial and fungal growth.

Seed quality
Seed quality is an important parameter that is critical for successful transplant and crop production. High quality seeds have higher germination percentages as compared to old seeds that often have poor germination and reduced vigor which leads to lost uniformity, revenue and productivity. If using older seeds, perform germination tests preferably a month before the actual start date of transplant production. When purchasing new seeds, growers should purchase seeds from reputed and trusted seed firms and select cultivars that are adapted to ones area and growing conditions.

Growing media
Vegetable growers have the option of using soil mixes or artificial mixes when producing vegetable transplants. The best growing medium is the one which has good moisture-holding capacity, good drainage, and high nutrient retention capability. There is a huge selection of various soil-less commercial media available for transplant production. These soil-less mixes are sterile, easier to handle and in addition carry small quantity of start-up fertilizers for initial seedling growth. In case of soil mixes, it should be made sure that the soil is sterilized, light, well drained and free of herbicide and pesticide residues. A soil test could be useful to correct for pH and fertility problems.

Irrigation management
The success of transplant production can be stymied by improper irrigation management. Proper irrigation management is crucial to produce strong, sturdy and healthy transplants that grow well and yield a quality crop. Some things to consider while making irrigation decisions are when,
how, and how much to water. In early stages of seed germination it is critical that the media is kept moist at all times. As the seedlings grow roots and get established water the plants only when moisture is needed. Water should be evenly distributed across the flats and uniformly applied without missing corners of flats and benches. Irrigation schedule would depend on plant species, flat or container size, crop growth, and prevailing environmental conditions inside the greenhouse. Over-watering, a very common error, results in restricted root growth and poor quality plants that are susceptible to insect pest and diseases. Over watering often promotes growth of fungus gnats and certain diseases especially damping-off. It is a good practice to water the plants in the morning, to permit foliage and soil surfaces to dry before evening. Plant water uptake is influenced by cloudiness, sunlight, and temperature thus water sparingly on cloudy days.

Nutrition management
Fertigation, or the use of water-soluble fertilizers at the time of each watering, is a common method of fertilizing vegetable transplants. No generalized fertilization regimen is available but a common alternative include a 75 to 100 ppm N solution applied twice weekly, or a 300 to 500 ppm N solution applied once a week. If higher concentrations of fertilizer are used periodically, it is recommended to occasionally flush the root zone in order to mitigate salt accumulation. Adjust fertilization according to temperature and light conditions. Tall and leggy transplants are produced as a result of low light conditions coupled with high fertilizer rates, and/or over watering.

Greenhouse lighting
In the northern climate zones like the Midwest, short day lengths lack of sufficient quantity of light during spring season can adversely affect transplant production and limit plant growth. High-pressure sodium lamps (400 watt) are commonly used for supplemental lighting in greenhouses; however, escalating energy costs make their use cost-prohibitive. Research is ongoing in various US universities including Michigan State on standardizing and optimizing the use of LED (Light Emitting Diodes) lights for use under greenhouse conditions.     

Pest and diseases
Warmer temperatures inside greenhouses promote optimum transplant growth but also create environment for rapid growth and development of pest and disease populations. The best approach to keep greenhouse clean and transplants free of pest and diseases is to develop a management plan based on sanitation, monitoring, and understanding of pest and disease life cycle. A good article to read in this regard is the article on integrated pest management in greenhouses on ATTRA website ( Three insect pests that present the largest routine problems in the greenhouses are white fly, thrips, and fungus gnats. Disease organisms that cause root rots are also a grave concern as initial phases of seed germination and the early stages of seedling growth are highly susceptible. The best control for pests and diseases is proper greenhouse sanitation, proper formulation of the growing media, proper irrigation scheduling, fertilization practices, and constant monitoring and removal of infested or infected plants. A number of disease problems can be minimized by keeping the water off the foliage and low level of relative humidity in the greenhouse. Under severe outbreak of pest and diseases selective insecticides and fungicides should be used according to labeled rates and timing.

Hardening off
Plants should be acclimated to the shock and stress of transplanting into the field by hardening them off. This can be achieved by removing the optimum growing conditions of the greenhouse by reducing the amount of water and/or fertilizer and reducing greenhouse temperature by 5-10 degree F. Alternatively transplants can also be hardened by moving out of the greenhouse and placing them in a lath house for a week or two before transplanting. Hardened plants can rapidly recover from transplant shock and better withstand adverse field conditions such as low temperatures and high winds.

Monday, March 4, 2013

Tomato Grafting and Pest Management Workshop

Ajay Nair
Department of HorticultureIowa State University
Tomato Grafting and Pest Management Workshop
Ames, IA. Come learn how to graft tomatoes and manage insect pests and diseases in your tomato plantings. This workshop will provide information and show proper techniques of grafting and handling of grafted plants. The workshop will also cover insect and disease management in tomato production. There will be live plant samples to learn how to identify pests, diseases, and their symptoms. Master gardeners, general public, and commercial vegetable growers will find this workshop beneficial as it will provide hands-on grafting experience. The event is scheduled for 12 March, 2013 starting 9:30am at Reiman Gardens, Iowa State University.


Welcome, registration and coffee
10am - 10:45
Basics of tomato grafting: Advantages and techniques – Ajay Nair, ISU
10:45 - 11:30
Hands on Grafting Exercise – Ajay Nair and Brandon Carpenter, ISU
11:30 - 12:30
12:30 - 1:15
Managing tomato diseases – Erika Salaau-rojas, Plant Diagnostics, ISU
1:15 - 2:00
Insect pests of tomatoes and their management – Laura Jesse, Plant Diagnostics, ISU
2:15 - 2:30 pm
Discussion, Evaluation, Adjourn

This event is sponsored by ISU Extension and Outreach, the Leopold Center for Sustainable Agriculture, and the Practical Farmers of Iowa.To register please click the link below. Registration is $35 per person. Seats are limited so please register by 03/10/2013. For more information on the event please contact Dr. Ajay Nair (; 515-294-7080).

Tuesday, February 26, 2013

It could be salty out there !

Ajay Nair
Assistant Professor, Department of Horticulture
Iowa State University

High tunnels are simple, plastic-covered, greenhouse-like structures that are passively ventilated and heated and the crops are grown directly in the soil. Over the last 4-5 years, an increasing number of fruit, vegetable, and flower growers have added high tunnels or are considering adding them to their farming operation to extend the season in the spring and fall. High tunnels have become an important tool for Iowa’s specialty crop producers to extend the growing season, increase production of quality crops, and increase profitability.

The environment without rainfall, limited space, and potential climate control in a high tunnel calls for unique set of crop management skills and serious attention towards management of soils. Both chemical and biological properties of soil, associated with continuous crop production inside high tunnels, can substantially change over short course of time. An important issue most growers are reporting is the buildup of excessive salts inside high tunnels. This is due to continuous application of synthetic fertilizers, animal manures, or manure-based compost in high tunnels. Intensive use of water soluble fertilizers of N, P, and K which are salts of respective nutrients significantly contributes to the salinity issue. Composts and manures high in salts can substantially increase soil salinity especially when they are applied in large amounts. The salt is often visible as a white crust on top of the soil (Figure 1). The issue salt buildup is compounded by the lack of precipitation inside high tunnels which prevents leaching of salts.  A build-up of salts over time leads to poor seed germination, causes salt injury including burnt leaf margins, stunted plants, reduced plant vigor, and reduces crop yield. Nutrient uptake and other metabolic processes can also be disturbed by soil salinity.

Fig. 1 Salt crust on soil aggregates inside high tunnels

One way for growers to keep track of salt levels is to regularly test their soils. Soil testing at least once a year will provide data on soil nutrient levels for proper nutrient management and help monitor soil attributes such as pH and salinity. Salt concentration in soil is estimated by testing the electrolytic conductivity (EC) of the soil. Soils with higher salt concentration have increased EC as compared to pure water which does not conduct electricity that well. There is lot of information available on ranges of soil EC that are detrimental to plant growth and cause plant injury; however, information on the method applied to measure EC is equally important to know. Depending upon method used, EC values change and so do the interpretation of those values. Three methods are generally used to measure soil EC.  The saturation paste extract method (SPE) is the most commonly used laboratory procedure for determining conductivity. In this method the soil sample is saturated with distilled water and mixed to a paste consistency. After letting the paste stand for one hour, the electrical conductivity of water extracted from the paste is measured using electrodes. A variant of this method involves measuring conductivity from a 1:1 or 1:2 soil-water mixture. In this case EC is measured after 15-20 minutes of shaking. The latter methods take less time but often are not as well related to the soil solution as is the SPE method. Electrolytic values from the 1:1 extracts are typically lower than those of SPE extracts due to increased dilution. Despite the differences in results between the two methods, many soil salinity samples are analyzed using a 1:1 extract because of reduced monetary and time investments. A conversion factor is used to convert EC values between two methods; however, value of the conversion factor is influenced by soil texture and organic matter content of the soil. A general rule of thumb to convert EC value obtained from 1:1 method to SPE method is to multiply by 2. So, an EC value of 1.5 dS/m from 1:1 method is equal to 3.0 dS/m in the SP method. Most plant responses to salinity levels reported in literature are based on values obtained from the SPE method. Table 1 shows various levels of EC at which plants show salt stress symptoms.

Table 1. Electrolytic Conductivity values from Saturated Paste Extraction method and respective plant responses
Electrolytic conductivity (dS/m)
Plant Response
0 - 2
Optimum plant growth
3 – 4
Plants show initial stress symptoms; smaller leaves
5 – 7
Growth affected; smaller and distorted leaves; reduced yields
Detrimental to plant growth; plant death; only salt tolerant plants can survive

Different plant species have various levels of salt tolerance levels (Figure 2). Plants with higher drought tolerance typically handle increased soil salt concentrations better than more drought susceptible plants. Table 2 below provides information on threshold values beyond which crops would show reduction in yields.

Fig. 2 Salt stress symptoms on pepper crop

EC (dS/m)
Sweet corn
Pepper (bell)

High tunnel growers should periodically check their soils for salinity issues and take steps to prevent high salt build up. Under high tunnels, investment per square foot is high and any crop damage or injury would significantly reduce profitability of the production enterprise. Below are some steps growers could take to prevent salt build up in their high tunnels

1.      Flush out salts periodically. This can be done by removing the cover, leaving the tunnel open, or flooding the tunnel with water to leach out salts. Flooding could be an expensive option, but leaving the tunnel sides open during the winter months is less expensive and doable. This would allow the snow to get in (certainly in a windy area for which Iowa is a strong contender). Alternatively when changing tunnel cover every 3-4 year, it could be left open for a period of time for the natural precipitation to get in
2.      Provide adequate drainage inside the high tunnels.
3.      Use of cover crops to improve soil organic matter and soil structure, reduce compaction, and improve drainage (installation of drainage tile pipes)
4.   Judicious use of water soluble fertilizers and compost.