Sunday, July 22, 2012

What is happening to the blossom end?

Ajay Nair
Department of Horticulture, Iowa State University

Lately a number of growers are finding small black spots, often with black concentric rings, on their tomato and pepper fruits. This is a typical symptom of a physiological disorder called blossom end rot. It is caused by lack of calcium uptake from the soil and transfer to the fruits during dry weather. The first symptom of rot is a slight water-soaked area near the blossom end of the fruit. This lesion soon darkens and enlarges in a constantly widening circle until the fruit begins to ripen. The affected area begins to turn black from colonization by saprophytic Alternaria fungal species.  Such fruits become non-marketable and could lead to significant losses. 

Calcium ions mostly move with water in the transpiration stream, up the xylem vessel, toward the upper plant parts. With current drought conditions and moisture stress, plants are not getting enough water and this directly affects calcium uptake. Calcium uptake by fruit can also be affected due to excessive nitrogen fertilization which leads to rapid shoot growth. Rapid shoot growth, occurring simultaneous with fruit growth, causes calcium to preferentially move into growing leaves as opposed to fruits, primarily because of higher transpirational pull from leaves. Transpiration pull from fruit is lower as they are covered with waxy coating. Below are some measures which growers/gardeners could take to mitigate blossom end rot:

1. Supply adequate water especially during high stress period (heat and drought). Uniform watering is critical for a steady flow of water in to the plants
2. Eliminate any other stress (insects, diseases, etc.) by addressing those issues promptly 
3. Avoid excessive use of nitrogenous fertilizers
4. Provide calcium to the plant (calcium fertilizers like calcium nitrate, calcium chloride, or various chelated calcium fertilizer materials). Foliarly-applied Ca fertilizers are not likely to correct or prevent blossom end rot

Sunday, July 15, 2012

Hornworm season

Ajay Nair
Department of Horticulture, Iowa State University

Past few weeks growers have been experiencing foliar damage in solanaceous crops, especially tomatoes and pepper. When observed closely one can spot large green colored caterpillars defoliating the plant. These caterpillars are commonly called hornworms and are fairly common this time of the season. It is extremely important to manage this pest immediately as these are voracious feeders and can defoliate the whole plant in a matter of few days (usually when more than 2 caterpillars present on one plant). The caterpillars blend in with the foliage and are not easy to detect and are often not observed until they cause considerable damage.
Hornworm camouflaged in the pepper plant
There are two kinds of hornworms, tomato and tobacco hornworm, although they are very similar in appearance and biology. The most striking feature of the hornworm is the presence of a "horn" located at the terminal end of their abdomen. This horn is usually "red" in color for the tobacco and "black" for the tomato hornworm. This is an easy way to identify them. There are on an average 2 generations of this pest in Iowa. The adult is a grayish white moth. Most of the damage is caused by the caterpillar and so it has to be controlled at that stage.

Tomato hornworm (notice the black horn) 

Adult tomato hornworm moth (picture courtesy Univ. of Florida) 

A number of synthetic and organic insecticide are available to manage this pest. Some of the common synthetic insecticides are  Asana XL, Sevin, Mustang, and Pounce. Within the synthetic group there are insecticides that have reduced impact on the environment, are less toxic to non-target organisms and humans, and have low pest resistance potential. Some of these reduced risk products include Intrepid, Entrust, Avaunt, and Coragen. Biopesticides have also shown excellent results in managing hornworms. A biological control organism that is highly effective and sold commonly is Bacillus thuringiensis (Bt). Some commercial Bt formulations include Dipel, Biobet, Javelin, and Thuricide. Please follow pesticide instructions accurately while handling the product.