DIAMONDBACK MOTH: The diamondback moth is one of three caterpillars that feed on crucifers. The cabbage looper is less common and the imported cabbage worm is so common everyone knows to look for the white moths and the large green caterpillar and its damage. But, even though the diamond back moth has only spotty occurrence when it does occur its damage is devastating and growers must know to look for it and manage it.
The tiny caterpillar, which is sort of pointed at both ends and is green and has a dark head and wriggles when disturbed, eats holes in the leaves……lots of holes. Leafy crops such as kale is quickly ruined. The adult sort of looks like a jet plane to me, except with folded wings and is flighty and hard to find.
The pest does not overwinter here in Maine. Moths are carried north on favorable winds and I have seen them in two locations near the coast this year. Even small infestations should be controlled because they can build to epidemic levels in just a generation or two and 3-5 generations in a season can occur.
Bt works well on the larvae. Bt works well on all three caterpillars, but remember only spray when the pest is there and you need to control it. Entrust works well too, but is quite expensive in comparison to the permitted Bt products.
Also, be sure to destroy crops after harvest so they do not serve as a breeding ground of future generations.
HORNWORMS: Hornworms are probably the most destructive insect attacking tomatoes and they are out in force now both in hoophouse and field tomatoes. They are giant caterpillars that can do a vast amount of eating in a very short time. Sometimes it seems that overnight healthy looking tomato plants are striped of their leaves leaving bare stems. The hornworms will also attack the fruit eating gouges out that look more like bites of a furry animal than an insect. Look now for the damage and the frass which is black pellets laying all around plants hosting hornworms.
The adults are large, fast flying hawk moths, which in flight may look like a hummingbird. At dusk they hover over flowers sucking nectar. Eggs are laid on tomato leaves and hatch in 5 days.
Hand picking is a bit frightening but does work and chickens enjoy fighting with the challenging pest. The problem is that they blend in very well and it is easy to overlook one or two caterpillars that can do significant damage in a day or two.
Bt works very well on this caterpillar, especially when they are small.
What Are Those White Things On Tomato Hornworms?: Tomato hornworm larvae are parasitized by a number of insects. One of the most common is a small braconid wasp, Cotesia congregatus. Larvae that hatch from wasp eggs laid on the hornworm feed on the inside of the hornworm until the wasp is ready to pupate. The cocoons appear as many small white projections protruding from the hornworm‚s body. Parasitized hornworms should be left in the field to conserve the beneficial parasitoids. The wasps will kill the hornworms when they emerge from the cocoons and will seek out other hornworms to parasitize. (reprinted from 2005 Vermont Veg and Berry News by Vern Grubinger)
CORN EARWORM REBOUNDS: [reprinted and modified from the sweet corn newsletter by David Handley]
Fall Armyworm Also Increasing - Protect Silking Corn!
Situation: Early corn harvest is coming into full swing in southern Maine. Development of later corn continues to be rapid with warm weather and good moisture. Insect pressure has increased in most locations this week, which was to be expected with several storm fronts moving in from the south and west during the weekend, carrying moths with them.
European Corn Borer: Moth activity is still low around the state this week, with the notable exception of Lewiston/Auburn and surrounding areas. Larval feeding damage has been fairly low in most fields. Sprays on pre-silking corn for feeding damage exceeding the 15% action threshold were recommended in East Corinth, Oxford, Poland Spring, Wayne and Wells. A spray to protect silking corn from corn borer based on moth captures in pheromone traps was only recommended in Palmyra. Other locations where corn borer moths were over the 5/week threshold were already being sprayed for corn earworm, so no additional sprays were necessary.
Corn Earworm: Moths captures in pheromone traps rose significantly in most locations this week, putting nearly all fields on a spray schedule for silking corn. This week a six-day spray interval to protect silking corn from corn earworm was recommended in Charleston, Lewiston, Oxford and Sabattus. A 5 day spray interval was recommended in Biddeford, Dayton, Dresden, Nobleboro, North Berwick, Readfield and Wayne, and a 4 day spray interval was recommended at in Auburn, Cape Elizabeth, Dayton, East Corinth and Levant. Corn earworm pressure may still increase with any weather fronts coming from the south.
Fall Armyworm: Moths captures in our pheromone traps increased significantly in many locations this week, so we can expect feeding injury from this pest (large ragged holes) to start becoming more prevalent. When feeding injury is found on pre-silking corn it is combined with any European corn borer feeding to determine if control measures are needed. When both types of injury are found on pre-tassel to silking corn, a spray is recommended if the damage is found on more than 12% of plants scouted. Fall armyworm moths may also lay their eggs on leaves of silking corn, allowing the larvae to move into the ears without leaving any visible feeding signs on the leaves that would be observed while scouting. Therefore, if more than 3 moths are caught in a week in a silking field not currently being sprayed for corn earworm, a spray to prevent fall armyworm infestation is recommended. This week, fields in Poland Spring and Wells had enough fall armyworm moths (3 or more) to justify a spray on silking corn that wasn't already being sprayed for corn earworm. XenTari® (Bt-for light infestations) and Entrust® are two materials that offer control and are approved for organic producers.
See the Resource Guide for Organic Insect and Disease Management or the 2006-2007 New England Vegetable Management Guide for details on these pests.
ONION PURPLE BLOTCH: This disease is caused by the fungus Alternaria porri and first shows up as lesions on the leaves that quickly develop white centers. As the lesions enlarge they become brownish purple and get to be an inch or longer. Spores are formed in the lesions and develop quickly in high humidity and warm temperatures. Alternating high and low humidity favor the spores release and they become airborne. The spores do not live long after they are released but when wind moves the spores on to new onion tissue and it is damp from rain, they germinate. The fungus survives between seasons on crop debris.
If this is a regular problem for you I suggest you try a biological control material called Serenade next year. It is a bacteria (Bacillus subtilis) the has proven to sometimes work well against this fungus. See the Resource Guide for Organic Insect and Disease Management for details on this material and efficacy reports. Also, be sure to rotate to a new field free of onion debris as far away from the old field as possible. In years where water is from irrigation instead of never ending rain, make sure to irrigate in ways that minimize hours of leaf wetness. Copper based fungicides may give you some control this season.
SQUASH BUG EGGS ARE HATCHING: The beautiful, copper colored squash bug eggs that you have been looking at on the squash leaves are hatching like crazy now. The nymphs are tiny and numerous. This is the most likely time that Pyganic will do a good job on them, and hitting them before they do damage is a good idea.
Remember, crop rotation and sanitation is critical to keeping populations of this pest small. Next year avoid putting cucurbits back in the same field or near the field where they are this year. Destroy crop debris and hiding places near the fields.