Dangers that lurk beneath Field pea producers are no strangers to common crop threats such ascochyta and aphids. But other pests, including the pea leaf weevil, have caught even the most experienced producers by surprise. How well do you know the dangers that lurk in your pea fields?
ASCOCHYTA COMPLEX BLIGHT
There are three basic ascochyta fungi that contribute to this ascochyta complex blight. The fungi develop during the growing season under cool, wet or humid conditions. Lesions form on green tissue — usually the leaves, stems, and tendrils — inhibiting the production of starches and sugars that are essential for good seed fill. The end results are lower yield and reduced seed size and quality. Because the stems are weakened, the crop may also lodge, making combining more difficult. Early symptoms of ascochyta can generally be observed under the plant canopy. Lesions start as small purple or brown flecks that grow and eventually compromise the plant. If the plant does survive, the peas produced will be small.
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APHIDS
Aphids also thrive in humid conditions and periodically appear in large enough quantities to warrant spraying. While aphids are more common on lentils, significant populations were observed in Saskatchewan pea fields in 2011. Aphids generally appear on peas during the flowering stage and when the pods are young. Insects are easily detected by putting one hand into the crop canopy and shaking the canopy with the other hand. If aphids are present, the sticky, green insects will fall into the palm. “Some aphids have the capability of wintering over,” said Scott Hartley, provincial specialist in insect management with Saskatchewan Agriculture. “Generally, they are a result of a “blow-in” from the south, but with a good snow cover to provide an insulation barrier, they can survive.” The best control option for aphids is a chemical foliar spray, preferably a dimetholate insecticide that offers systemic and contact control.
PEA LEAF WEEVIL
The pea leaf weevil is a relative newcomer that has recently established residency in southwestern Saskatchewan. It has been observed in Alberta for several years and was first spotted in Saskatchewan in 2007. Since then it has been migrating gradually eastward, but is still most prevalent in pea and faba bean fields in the southwest. The pea leaf weevil overwinters as an adult beetle and emerges in the spring to feed on tender new pea leaves. Feeding causes distinct notching or scalloping on the leaves. The adult female lays eggs in enormous numbers and the resulting larvae feed on the pea’s nitrogen fixing nodules, eventually destroying the plant. Pea leaf weevils are most effectively controlled by seed treatment and foliar spray. Fields may benefit from the application of supplemental nitrogen. The pea leaf weevil should not be confused with the pea weevil, which occasionally develops in dry pea storage.
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