Agriculture Reference
In-Depth Information
Insect and Disease Influence on Corn and Soybean Production
The intensification and mechanization of grain production can increase crop
susceptibility to plant pathogens and insect infestations because it provides
extensive resource opportunities for these organisms. Major disease outbreaks
are rare but can have significant impacts on corn production in the NCR. In
1970, for example, the Southern Corn Leaf Blight—caused by the fungus
Helminthosporium maydis
(Nisikado & Miyake)—resulted in a 10% reduction
in national corn production, the largest decrease in corn yield due to a pathogen
in U.S. history. The outbreak was limited to 1 year and was attributed mainly to
an uncommon combination of favorable environmental conditions for the fungus
(Tatum 1971).
Soybean production in the United States has been largely unaffected by dis-
ease, although a recent arrival introduces the potential for significant harm. Asian
Soybean Rust, caused by the fungus
Phakopsora pachyrhizi
(Syd. & P. Syd.
1914), was present for many years in Asia before spreading to Africa and South
America (Miles et al. 2003). This fungus was found in 2004 at a research farm
in Louisiana (Schneider et al. 2005). Isard et al. (2005) produced a soybean rust
aerobiology predictive model that guided soybean rust scouting operations after
its initial discovery. Predictions of soybean yield decline are as high as 80% in
the absence of effective management strategies, such as fungicide sprays now
common in Brazil. Major research efforts are under way to develop more effec-
tive fungicides and disease-resistant soybean varieties. Although its impact in the
United States thus far has been limited, this disease remains a significant threat
to soybean production.
Insect pests have also affected corn and soybean yields. The European corn
borer has plagued corn producers, who have waged major pesticide assaults against
the insect. The borer can also be managed by rotating crops to break the insect's life
cycle, and by cutting cornstalks close to the soil surface at harvest to remove over-
wintering habitat. Corn varieties with genes inserted to produce the bacterial toxin
Bacillus
thuringiensis (Bt), fatal to the larvae of moths and other lepidopterans,
provide protection for 65% of U.S. corn acreage (ERS 2011b) at a disputed envi-
ronmental cost not fully resolved (Rosi-Marshall et al. 2007, Beachy et al. 2008,
Parrott 2008, Jensen et al. 2010, Tank et al. 2010).
The western corn rootworm (
Diabrotica virgifera virgifera
LeConte) is another
serious corn pest responsible for severe root damage and subsequent yield loss
when large populations are present. Insecticides applied to soil can reduce infesta-
tions but are costly. Although crop rotation can also be effective at reducing infesta-
tions, the rootworm has adapted to the normal rotation of corn and soybean in the
NCR (Levine et al. 2002), so rotating into soybean is no longer an effective control
technique. Bt genes have also been inserted into root tissue to combat rootworm,
offering another pest management option for farmers. While such genetically modi-
fied crops have provided benefits to both agriculture and the environment, weed
herbicide resistance is an important emerging problem (NRC 2010a) and questions
remain regarding the long-term ecological effects of using genetically modified
crops (NRC 2008, NRC 2010a).
