Field Crops

Natural Control of Budworm and Bollworm in Texas Cotton

While undergoing the eradadication of boll weevil from Texas, it was realized that there was significant potential for improved natural control of budworm and bollworm because of the reduction in insecticide usage. Research conducted in four regions of Texas: southern and northern Blacklands, Trans-Pecos, and High Plains, was reported in 1997. Results indicated that usually more than 85% of bollworms died in the egg stage, and egg and larval mortality combined reached over 95%. Egg parasitism contributed insignificantly to mortality, and attempts to determine the role of predators were often inconclusive. However, the amount of mortality was consistent across the entire Texas cotton belt.

Source:

Smith, J. W., et al. 1997. Natural control of budworm/bollworm in Texas cotton, p. 5-6. In: Knutson, A., and J. Smith, ed. Biological control program, 1996-1997 report. Texas A&M University, Dept. of Entomology.

Artificial Habitats Boost Predator Populations in Soybean

Predation by generalist predators, such as spiders and ground beetles, can reduce pest damage in many crops. Providing temporary refugia during cyclical farming disturbances has been used in China for more than 2000 years to encourage spiders, but this technique has not been systematically investigated on a larger scale in western-style agriculture.

After conventional tillage of soybeans, populations of spiders and their egg sacs normally decline by up to 75%. When modular habitats, consisting of chicken wire loosely filled with bedding straw, were placed in tilled fields, there were 5 to 36 times more spiders compared with open fields, and spider egg sacs were 18 to 87 times more abundant. Spider diversity was also much higher, with 60% more species found in refugia than in the open field. There were also more harvestmen, ground beetles, and rove beetles when refugia habitats were provided.

Throughout the season the microhabitat within the refugia is more favorable for survival of predators than in just soybean plants or weeds. For example, in early Ocotober, harvestmen were 90 times more abundant in refugia than in senescing soybeans. The refugia supply not only a place to live, but may also enhance the predators' food base. Small arthropods feeding primarily on fungal hyphae and detritis present in the decaying straw, especially Collembola (springtails), were available as alternate prey.

Spider populations peaked earlier in the growing season in refugia, at a time when herbivore control may be more critical for plants. Soybean seedlings grown within a yard of these modular habitats had 33% less damage than plants in areas without habitats (although this did not significantly increase soybean yield).

Using temporary habitats can conserve naturally occuring predators to enhance pest control. Providing special habitats, such as the chicken wire cages used in this research, would only be feasible on a small scale, but mechanized distribution of discrete straw patches in a field after tillage or harvest operations may offer some benefit on a larger scale.

Source:

Halaj, J., A. B. Cady, and G. W. Uetz. 2000. Modular habitat refugia enchance generalist predators and lower plant damage in soybeans. Environ. Enomol. 29(2): 383-393.


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