Insect populations fluctuate greatly with temperature and moisture.
Year 2016 was an interesting one that started with a very wet spring followed by a drought starting in June with a dramatic reduction in precipitation that lasted five months. Looking at climate data from Clanton, Ala., as an example of what happened last year, after the last big rain event in June 2016, the total rainfall was a mere 3.9 inches from July to November, a shortfall of 18.5 inches. This was stressful for producers and underscores the critical nature of our water resources. Many northern parts of the state had worse rainfall records, and the struggle continues for many farmers in the state.
Insects Prefer Drought
Unfortunately, insect pests took full advantage of the hot, dry summer months that favored shorter development periods and intense migration between crops. In the graphs below, we have summarized the insect pest population fluctuations based on sticky wing insect traps from multiple locations, including Clanton.
The cool, wet spring with frequent rainfalls from January through May appeared to delay the activity of several moth species such as corn earworms, loopers and some armyworm species. However, moth activity significantly increased in peanuts and vegetables once the drought hit us in mid-summer. We noticed the largest spike in the activity of fall armyworm, soybean looper and the lesser cornstalk borer in August and September. We generally see a late-season migration of fall armyworms–a highly migratory pest–from hay and pasture fields to vegetable crops.
Record LCB Moth Catch
In 2016, this behavior created an extra heavy pressure made worse by the drought that may have affected crop yield. Direct crop scouting in research plots also indicated an unusually high number of armyworms actively feeding in the crops along with soybean loopers. The lesser cornstalk borer, a major peanut pest, becomes a major issue during drought and our traps removed nearly 5,000 moths in four months–the highest ever on our record.
Extreme drought also pushes insects to seek moisture in soil around plants, and that can really mess things up for farmers. Caterpillars and pests like the burrower bugs in peanuts, which may enter the soil cracks to escape heat and get moisture, are very difficult to kill with any organic or conventional contact insecticide.
It was also intriguing to find a very prolonged squash vine borer activity in vegetables with nearly three overlapping generations detected over the year. Tobacco budworm moths were detected at 70 to 80 percent of our pest monitoring locations with very high trap catches in north Alabama.
Always Consider Spider Mites
Hot dry weather also favored spider mite outbreaks. Indiscriminate spraying of crops with synthetic pyrethroids can worsen spider mites in peanuts and vegetables by removing beneficial mites from the ecosystem. An aggressive spider mite outbreak is the worst problem than all other pests combined and crop loss in peanuts can be over 30 percent in uncontrolled conditions – so be cautious in developing your IPM plan during stressful weather.
Know What To Expect
Lastly, when in drought, don’t forget to scout using the proper sampling techniques and tools. Producers should check the Alabama Peanut IPM or the Alabama Vegetable IPM website for a complete listing of crop scouting manuals. Hay producers are encouraged to contact Dr. Kathy Flanders and refer to her blog article on armyworms. Consult with the agronomy or commercial horticulture regional Extension agents for assistance with insect pest identification and to develop site-specific IPM plans.
Insect pest populations fluctuate greatly with temperature and moisture levels. Please check the USDA Drought Monitor regularly and find the condition in your county. For details, visit http://droughtmonitor.unl.edu/Home/StateDroughtMonitor.
Article by Ayanava Majumdar, Extension Entomologist, Gulf Coast Research and Extension Center, Fairhope, Ala., and Neil Kelly, Rudy Yates and Monte Baugh, Alabama Cooperative Extension Service Regional Extension Agents.