Resource Guide for Organic Insect and Disease ... - Cornell University

ORGANIC INSECT AND DISEASE CONTROL FOR
Legume crops
40 Organic Resource Guide
INTRODUCTION
Legume crops belong to the family of flowering plants known as Fabaceae. Sometimes the
family is referred to as the Leguminosae, or legumes. The unifying characteristic of the family
is that the fruit, often called a pod, has a single chamber and opens along two edges. Pods
typically contain more than one seed. This family is very diverse and includes both trees
and herbs. Worldwide, it is among the most important plant families for food crops. In the
northeast region, the two most commonly grown legume food crops are peas and beans.
I. INSECT CONTROL__________________________________
APHIDS
The pea aphid has traditionally been the only significant aphid that attacks peas. Fava beans,
alfalfa, vetch, and clover are also hosts. Populations are usually small, and there is little damage
during vegetative growth of peas; however, aphid populations may increase at flowering.
Especially during pod-fill, feeding can result in smaller seed size and fewer peas per pod.
Additionally, the pea aphid can transmit viruses.
Populations of pea aphids may build rapidly in late June and early July. Later in the pea
season, aphids may either leave the planting for perennial hosts or die when the peas are
harvested or senesce. Sexual forms appear on perennial hosts in August and September and
lay overwintering eggs on the plant stems. Alfalfa, vetch, and clovers are common sites for
overwintering eggs.
Additionally, the recently invasive soybean aphid can be a pest on snap bean. While feeding
rarely causes direct damage, colonizing aphids are a serious vector for viruses, especially
cucumber mosaic virus. If plants are small at the time of colonization, feeding by adults can
cause leaves to curl downward and may temporarily stunt plant growth. Infested plants will
outgrow these symptoms, and because snap bean is not a suitable host for reproduction, the
colonizing aphids will eventually disappear. Treatment is rarely, if ever, warranted.
Cultural Control:
1. In the fall, harvest or mow alfalfa, vetch, and clovers that are near fields that will be
planted with peas or snap beans during the following spring. This practice reduces
overwintering aphid populations.
2. Since soybeans are attractive to aphids, avoid planting late-season snap bean fields
near soybeans.
3. Maintain habitat for natural aphid enemies including lady beetles, lacewings,
predatory midges, and parasitic wasps.
Materials Approved for Organic Production:
Aphid populations should be monitored when peas begin to flower. Action thresholds
recommended for conventional production are one to two aphids per leaf or two to three
aphids per stem tip and one per small pod. In organic production, a better approach may be to
monitor populations over a two to three week period before flowering, and treat if populations
continue to increase with no natural enemies present. If aphid populations are above
threshold, control may be warranted.
1. Soap: Ensure coverage of the parts of the plant where aphids live, especially the
undersides of leaves and fruit.
2. Neem: Azadirachtin-based neem products can provide some control.