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

By the time injury to the plant is noticed, yield loss cannot be prevented. The injury is not
reversible, and the plants are stunted at best; young plants may die. Monitoring the pest is
essential. Sweep nets are typically used to sample adults, while nymphs are sampled directly
on the underside of a leaf. A common threshold for determining if treatment would be cost
effective is an average of one nymph per trifoliate leaf or 50 adults in 10 sweeps with a net.
Cultural Control:
Since the PLH does not overwinter in the Northeast, crop rotation is of no value. Row covers
may be used to protect young beans until they flower, after which the crop is less susceptible.
Materials Approved for Organic Production:
Pyrethrin (e.g. PyGanic EC5.0) has been shown to be the most effective material available to
organic growers. Spray in the evening and be sure to get good coverage, especially on the
undersides of the leaves. Multiple sprays may be required because this material does not
persist.
CORN EARWORM, EUROPEAN CORN BORER, AND CABBAGE LOOPER
These occasional pests of beans can, in some cases, cause serious injury. The larvae feed on
the foliage, making holes in the leaves. When pods are present, they feed on the outside of
the pod and may burrow inside to feed on the seed. Avoid planting beans near corn, which
is a much better host for these insects. For serious, recurring infestations, mass release of
Trichogramma ostriniae may be worthwhile for controlling European corn borer. Release must
be timed to occur when eggs are present. This egg parasitoid will not affect corn earworm or
cabbage looper. Bt (e.g. DiPel 2X) and spinosad (Entrust) may be effective if applied before
caterpillars bore into the pods.
II. DISEASE CONTROL_________________________________
DISEASES CAUSED BY BACTERIA
BACTERIAL BLIGHT- Peas (Psudomonas syringae pv. pisi)
Bacterial blight of pea is a common problem that may reduce yields and scar pods during wet
years but is not a significant problem under dry conditions. It is not the same pathogen that
causes the bacterial diseases of beans, though it does have a wide host range including sweet
peas, hairy vetch, cow peas, and soybeans. Lesions may be found on any of the aboveground
parts of the plant. They begin as small, water-soaked spots that later develop brown margins,
become necrotic, and may grow together, causing the leaves to turn brown and die. The whole
crop may be lost if bacterial blight infection occurs during the seedling stage.
The pathogen does not persist in soil. The principal source of infection is infested seed. If
conditions are wet at planting time, the disease is more likely to be transmitted from the seed
to the developing plant. Subsequent spread within and between fields is possible by moving
water, machinery, insects, people, etc.
Cultural Control:
1. Planting clean seed is key to management.
2. Resistant varieties are available.
3. Seed raised in arid regions are less likely to be infected.
4. Avoid walking or working in pea fields when the plants are wet.
5. Promote good airflow and fast leaf drying by providing adequate row and in-row
spacing.
Materials Approved for Organic Production:
Copper fungicides can be effective in limiting secondary spread. See the copper fact sheet
(page 123) for a discussion of efficacy and minimizing accumulation in the soil.
44 Organic Resource Guide