Monday, August 29, 2016
ALFALFA CUT WORMS
ALFALFA CUT WORMS By Woods Houghton Eddy County Agriculture Agent Alfalfa fields across south Eddy County have been slow to recover from the third, fourth or fifth cutting. Some fields have no re-growth and in other fields the re-growth has been slow and plants are pale green and droopy. So what's going on? I think there are two main problems. The pale green, droopy plants nearly always are in fields that have had abundant rain. So much rain in fact, that the soil has remained saturated with moisture for many days in a row right after cutting. Alfalfa doesn't like wet feet. This is especially true right after harvest. For alfalfa to re-grow, oxygen must be available in the soil. Water-saturated soils have little or no oxygen available for the plants. As a result, re-growth is very slow because plant roots are suffocating. This reduces nutrient and water uptake by roots as well as metabolic activity for re-growth. These plants act just like plants that have not had water and they are weaker and more susceptible to insects and disease. The other problem has been insects. From alfalfa weevil larvae to army worms to cutworms to alfalfa caterpillars, it seems like everybody, somewhere has had enough of each of these insects to hurt re-growth from feeding on the newly developing buds. It only takes 3-5 cutworms per square foot to be considered economically damaging. Using insecticides to kill these bugs is about the only solution for any sizable acreage. Synthetic pyrethroids ,usually give the best control. Most producer like to use two different classes of insecticide after the 2010 infestation. If these worms aren't controlled, alfalfa yield and stands will suffer. I observed 4 worms per stem eating the green off the stem. These stands have been hit hard and some may not recover. Cutworms develop on rangelands or weedy fallow fields and move into alfalfa usually after the first cutting. Cutworms are nocturnal insects which feed at night and hide during the day in soil cracks and under debris and loose soil. Growers, pest control advisors, and crop consultants should vigorously scout for the worm at night or early in the morning. Light traps can be a useful tool to estimate the population based on the adults the traps attract. Irrigation or harrowing may help reduce the population at these high populations control will have also include insecticide applications. Subscribe to Eddy County Ag news at: http://nmsueddyag.blogspot.com/ Eddy County Extension Service, New Mexico State University is an equal opportunity/affirmative action employer and educator. All programs are available to everyone regardless of race, color, religion, sex, age, handicap, or national origin. New Mexico State University, U.S. Department of Agriculture, and the Eddy County Government Cooperating.