Heart-shaped leaf that doesn't want to leave !

Ajay Nair
Department of Horticulture, Iowa State University


Heart-shaped objects not always bring fun and joy to our lives, certainly not this one. This weed, Abutilon Theophrasti, commonly referred to as velvetleaf, buttonweed, wild cotton, or Indian mallow has been slowly invading soils under vegetable production. Flower and seeds are produced from July through October and the seeds can remain viable in the soil for about 20-40 years. The plant is 3-7 feet tall and has  large heart-shaped leaves usually 2 to 5 inches wide. Velvetleaf causes the most concern in row crops, however, it can create problems in vegetable production as well. The plant can compete with vegetable crops for water, nutrients and due to its erect growth habit can also shade plants in its vicinity.

It has been reported that leaves and seeds of this plant carry allelopathic chemicals that inhibit the germination and growth of crops, such as radish and turnip.  A number of pre- and post-emergent herbicides are available to control velvetleaf, but more importantly, steps should be taken to reduce its seed bank in the soil. Crop rotation, avoiding excess N application, and hand pulling small populations (remove from the field or burn, since the seeds will ripen after the plant is pulled) will help to control velvetleaf. Velvetleaf becomes less of a problem in no-till systems because if seed germinates on the soil surface, it dies. Some amount of biological control also occurs (velvetleaf seed beetle destroys developing seed; fallen seeds are eaten up by mice and ground beetles) but the best practice is not to let the plant go to seed and, if it does, then removal and destruction of the plant is the next alternative.

Snap Bean "Blossom Drop"

Ajay Nair
Department of Horticulture, Iowa State University


An interesting plant sample came in yesterday from one of the snap bean growers from Hancock County, Iowa. Apart from the description of a potential disease, which the plant diagnostic lab will figure out soon, the information sheet also contained a note: "The crop flowered profusely but is not bearing any pod". Pictures below show few to almost no pods on the plant.





This unusual event is called "Blossom-Drop" which is quite common in peppers, snap beans, and tomatoes.  There are multiple causes for this to occur such as dry windy conditions, excessive use of nitrogenous fertilizers, but the most common cause is high temperature. Tomatoes, peppers and beans are sensitive to prevailing air temperatures with regard to setting fruit. When the day temperatures are above 90 degrees, it affects pollen viability and thus adversely affects pollination. If the flower isn't pollinated, it dies and falls off.

Another important aspect to consider is irrigation. Green beans are particularly susceptible to blossom drop under water stress. Growers should carefully monitor crop water requirement and irrigate whenever needed (depending upon soil type). For growers confronting 'blossom drop', there will be some yield reduction but when temperatures turn cooler new flowers form which would set new pods.

Irrigation: worth an investment

Ajay Nair
Department of Horticulture, Iowa State University

Past 2-3 weeks have been extremely brutal in Iowa in terms of high heat and humidity. Most of our daily conversation revolves around 'heat index', a word we constantly hear on television. Plants, similar to us, have their saga to share. Extreme heat has taken its toll on them as well. Crop water requirements depend on crop type, stage of growth, and evaporative demand. In hot weather conditions plants transpire large amounts of water that needs to be quickly replenished to ensure continued growth and development. Failure to replenish water, can lead to several issues apart from wilting. Last week (25 July 2011) I was in the Western part of Iowa visiting some fruit and vegetable growers. One of the problems I noticed in tomatoes is in the picture below (click on the picture to expand):

According to Dr. Hank Taber (Professor Emeritus, Iowa State), the above pictures show what is called 'russetting' or 'micro cracks' in tomato fruit. This occurs under extreme hot conditions coupled with  lack of water for plant uptake. Tomato skin becomes patchy, rough, and develops cracks which can cover large areas on the fruit. Such fruits quickly become non-marketable and can lead to significant loss of revenue to the grower. To prevent this from happening growers should provide ample amount of water in a timely and controlled manner. Although, setting up and installing irrigation could be an expensive operation, it is a critical component for successful vegetable production. It is worth an investment which always pays off !

Tomato Leaf Mold

Ajay Nair
Department of Horticulture, Iowa State University

Tomato leaf mold is a fungal disease caused by Fulvia fulva. It occurs mostly under greenhouse conditions where relative humidity is high. When humidity is high, the fungus develops rapidly on lower leaves and
progresses upward. Significant yield reduction could occur if the fungus is not controlled early. Pictures shown below were taken in a greenhouse located near Cedar Rapids, IA in the second week of July 2011.

Symptom on upper side of leaves appear as small, pale green, or yellowish spots. On the corresponding lower side, the fungus sporulates producing darker colored area. Growers should consider taking following steps to manage tomato leaf mold disease:

1. Provide good ventilation in the greenhouse. Use fans to circulate the air inside
2. Whenever possible, keep relative humidity below 85%
3. While transplanting maintain adequate row and plant spacing to ensure sufficient air movement. Remove suckers to reduce shading and maintain proper plant growth
4. Avoid wetting leaves while watering
5. Reduce primary inoculum by disposing affected plant debris after harvest.
6. Some fungicides to control leaf mold include Dithane, Revus Top, Tanos, and Inspire. Use fungicides as per  label instruction and guidelines

Spray but not sway - Roundup damage on tomatoes

Ajay Nair
Department of Horticulture, Iowa State University

We are obsessed with things that are round.....cookies, pizza, pies, and now ROUNDUP !  Weed control had never been easy until the formulation called Glyphosate which is a non-selective, broad-spectrum, systemic herbicide and an active ingredient in Roundup. Care should be taken to minimize spray drift while applying this herbicide. Roundup spray drift can cause serious injury to non-target plants.

Pictures below show roundup damage on tomato plants growing inside high tunnels (compare with the rows behind). The entire row of plants growing on the outer edge of the tunnel was damaged due to roundup drift from adjacent field. Symptoms include distorted new growth with cupped leaflets. Extent of damage on tomato crop depends on factors such as  stage of growth, amount of exposure, cultivar, etc.

Precautions to avoid such damage:

1. Avoid spraying under breezy conditions

2. Utilize a shield to prevent drift over to non-target plants. 

3. When applying roundup near or in vegetable gardens, increase droplet size to minimize mist and possible drift.