Sunday, August 21, 2011

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.

Friday, August 12, 2011

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.

Tuesday, August 2, 2011

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 !