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

2. Crop rotation is recommended.
3. Plan to plant after the spring flight (sow after accumulation of 450 degree-days above
45 o F).
Materials Approved for Organic Production:
There are no materials approved for organic production.
TARNISHED PLANT BUG (Lygus lineolaris)
The tarnished plant bug (TPB) is a pest with a very wide range of hosts, including about three
hundred species of weeds and crops (Photo 9.2). In its earliest stages (i.e., nymphs), the TPB
resembles an aphid, though as it develops, it looks more like an adult TPB without wings. In
the umbels, it causes damage to celery stalks and leaves. This sucking insect causes cavities on
the stalk where tissue has collapsed. Feeding on the leafy parts of celery, usually by nymphs,
causes necrosis of the youngest leaves.
The tarnished plant bug overwinters as an adult in sheltered sites, such as edges of woods and
hedgerows or in crop residue. They become active in early spring and feed and lay eggs on
weeds and early-flowering crops, such as strawberries and alfalfa. Nymphs have similar feeding
habits and cause similar damage as the adult. There are two to three generations per year.
Cultural Control:
1. The best control of this pest is use of floating row covers installed at planting.
2. Managing weeds and keeping headlands mowed short helps. However, avoid mowing
nearby fields when crops are at a vulnerable stage, as doing so may drive the pest into
cropland.
3. Decades ago, a Braconid wasp, Peristenus digoneutis, was introduced in the United
States for biological control of the tarnished plant bug, and it has since spread
throughout much of the Northeast. Parasitism rates are reported to be as high as
70%, so using management strategies that conserve them, and other natural enemies,
should be helpful.
Materials Approved for Organic Production:
Insecticides have only limited effect on TPB because of the rapid re-infestation that occurs from
non-treated areas.
1. Pyrethrum gives limited control (40-60% control in the older literature; one poor result
in recent studies).
2. Neem has shown some promise, but more studies are needed (two fair results against
TPB in recent studies).
APHIDS (many species, especially the green peach aphid)
Aphids sometimes aggregate on celery, but infestation is not common on farms that do not
spray often with broad-spectrum insecticides. When present, the damage is seen as distorted
leaves.
Cultural Control:
1. Encourage natural enemies by diversifying the habitat in headlands and woods
surrounding the field.
2. Refrain from using broad-spectrum insecticides (see the Brassica Crop chapter for more
details).
Materials Approved for Organic Production:
1. Soap: Scout plantings once or twice each week, and if aphid populations are
increasing, apply insecticidal soap sprays. Do not wait until aphids reach high numbers
and dense colonies; apply when numbers are low. Repeat applications two or three
times, and ensure good coverage of the parts of the plant where aphids live, including
the undersides of leaves.
74 Organic Resource Guide