MOFGA Pest Report 2004
July 10, 2004

ONION AND GARLIC

Pink root is showing up in a number of sites around the state and in some case quite severe. It primarily effects onion and garlic but also can infect a wide variety of vegetables. I am seeing it in garlic quite bad in two sites. The first symptom you see will be the tops turning yellow or white and then wilt and die. The roots turn pink, then darken to red or purple. I confused the disease by the symptoms with Fusarium basal plate rot, which is pointed out in the literature to be common and at one time the two diseases were thought to be caused by the same organism, but one farm sent a sample to Bruce Watt at the UMO Pest Management office and he identified it as Pink Root. Pink root is caused by a fungus, which survives in the soil as various kinds of spores or in roots or plant debris. The fungus invades through the root tips. The fungus proliferates throughout the roots, but does not infect the basal stem plate or fleshy scales. Control is by rotation and it should be relatively long, 3-6 years. There are more resistant varieties.

White rot has also been identified by Bruce and this is an even more serious problem that is quite contagious. It is a serious disease of the Allium species. Symptoms on the foliage include premature yellowing and dying of the older leaves. A white, fluffy mycelial growth on the stem plate is and early symptom and it extends around the base of the bulb. The disease eventually moves inward from storage leaf to storage leaf. White rot is caused by the fungus Sclerotium cepivorum. The disease persists in the soil for many years as sclerotia (vegetative resting bodies) and when a host root grows nearby it is stimulated by chemicals released from Allium roots to germinate. Again, rotation is the best control. If incidence is low, pull infected plants and destroy. If the incidence is high then there will be lots of sclerotia left in the soil and a long rotation (8-10 years) is recommended. Ailsa Craig is a resistant variety and there are probably others.

BEETS- SCAB

The same scab that forms on potatoes forms on beets. It is caused by an organism that is classified as a fungus but has been classified as a bacteria in its past. It also effects carrot, parsnip, radish and turnip. The symptom is the same as potato scab, a warty, corky scab on the surface that may be pitted or depressed with the skin cracking. The root can be eaten but it has poor customer appeal and may be hard to market. The organism can be found even in virgin soil. It invades when the plant is young. It is less active in soils with pH below 5.7, but crops do not grow as well with such low pH. The bacteria can exist in the soil for many years. Water management is important as dry ground favors the pathogen and disfavors its antagonists. Avoid land known to be infested or droughty, land and fields where sawdust, wood shavings or ashes have been applied. Avoid rotations with potatoes.

LATE BLIGHT IN NEW YORK

(compiled from information from Tom Zitter and Carol MacNeil By Brian Caldwell)

Late blight samples were received today from two potato fields in Steuben County and are currently being typed as to genotype. This is very early for late blight to show up, and does not bode well for the season.

Growers have been advised to begin protective late blight sprays in Steuben and adjacent counties. Organic growers have the option of using approved copper fungicides, which have some activity against late blight, to protect their tomatoes and potatoes. Good coverage is essential for control.

Fields at greatest risk are those where there is frequent and long-lasting rain, dew, fog or relative humidity of 90%+, when temperatures are at least 59 degrees F. Ten hours of such conditions are needed for late blight spore production and infection. The longer the time, the greater potential for infection, if spores are present. Check cull piles to be sure there are no live sprouts!

In the morning while plants are wet with rain or dew late blight looks very black with spreading, irregular borders. A fine white fuzz of sporulation is often present. In the afternoon on a sunny day the lesions on leaves look brown with a prominant yellow green border and the sporulation will be dried. Lesions may appear first on leaves, stems, the growing point, or in the axils of the leaves. Late blight is an obligate parasite, meaning that it can only get established on live plant tissue. The disease can spread explosively when weather is favorable. If late blight is detected in a spot in a field destroying that infected area and a large border around it can help to prevent spread to the rest of the field. Once a late blight infection is established it's very difficult to stop. Late blight can spread long distances on winds, especially if humidity is high.

If you think you may have late blight place foliage in a blown up plastic bag and seal. Take it to your local Extension office for positive identification. Call me for more information.

No late blight has been reported in Maine, yet.

SWEET CORN REPORT

(modified from Umaine report by David Handley)

The 2004 University of Maine Cooperative Extension integrated pest management (IPM) program for sweet corn growers is underway. More than twenty volunteer farms are serving as pest monitoring and demonstration sites this year. Farm locations include North Berwick, Wells, Dayton, Cape Elizabeth, New Gloucester, Poland Spring, Auburn, Lewiston, Dresden, Jefferson, Nobleboro, Warren, Monmouth, Wayne, Oxford, Farmington, Levant, Stillwater, Garland and East Corinth. Pheromone traps have been set up at these locations to monitor the adult (moth) stages of European corn borer, corn earworm and fall armyworm. Fields at these farms are also being scouted for feeding injury by the larvae of these insects. Management recommendations will be based on all of the information collected and will be updated weekly. This information will be passed on to you through this newsletter every week for the remainder of the season. If you would prefer to receive this message via e-mail, give us a call at 933-2100 or send an e-mail message to: dhandley@umext.maine.edu. Detailed information is placed on the Pest Management Office web site at: http://www.umext.maine.edu/topics/ pest.htm.

SITUATION
Early corn planted under plastic mulch or rowcovers is well advanced and now silking in some parts of the state. Late planted corn has been a little slow to get established in some fields due to extended cool wet soil conditions. Many fields are now in the whorl to pre-tassel stage, and need to be scouted for early pest problems.

European Corn Borer: Pheromone trap catches indicate that we are experiencing a significant emergence of European corn borer moths. These moths are laying eggs on corn plants and the larvae are just beginning to feed on the foliage. European corn borer is the only one of the three major insect pests of corn that can successfully overwinter in Maine, and it is usually the first pest to become a significant problem. We typically scout 100 corn plants in each field, examining twenty plants in a row at five locations throughout the field. This sample provides a reasonably accurate estimate of the total amount of injury in a field. European corn borer feeding damage ("pinholes" in the leaves) has been found in all locations scouted this week, and has exceeded the control threshold in fields in Biddeford, Cape Elizabeth, Dayton, Oxford and Wells. We expect injury to increase in other locations soon. Corn in the whorl stage need only be sprayed if fresh feeding injury is found on 30% or more of the plants scouted in a field. Once the corn reaches the pre-tassel stage, the control threshold is lowered to 15%. This is because larvae feeding on the later stages are more likely to move into the ears of the plant. Sprays during the pre-tassel stage when moths and feeding are present can significantly reduce the opportunity for larvae to move into other parts of the corn plant, where they will be protected from future sprays. Good spray coverage of the plant provides the most effective kill of larvae as they move from one part of the plant to another. Rotating the type of insecticide used may also improve control. Both Dipel 2X and Entrust are registered for ECB control and organically approved.

When corn reaches the silk stage, as it has in a few locations this week, sprays may be based on the number of corn borer moths caught in pheromone traps rather than just feeding injury. European corn borer moths will lay eggs on flag leaves of silking corn and the larvae can move into the ears without leaving any visible feeding injury that would be noticed when scouting. Therefore, if more than five moths are caught in a week in a field with silking corn, a spray will be recommended. This week sprays on silking corn were recommended in Dayton, No. Berwick, Farmington and Poland Spring.

Corn Earworm: Only two corn earworm moths have been caught in our pheromone traps around the state so far this season (Cape Elizabeth and Lewiston). The capture of a single moth in a field does not warrant a spray, and no silking corn was present in these fields. Corn earworm usually appears in Maine around the second week of July, but the actual date varies greatly. The arrival of this pest is only a concern for fields with corn in the silk stage. Fields not yet in silk do not need to be protected from corn earworm. When corn earworm moths start being caught at a site, all silking corn in the fields should be protected with a spray. These moths lay eggs on the fresh silks and the larvae move directly into the ears of corn. When corn earworm moths cannot find silking corn to deposit their eggs on they may lay eggs on the leaves of younger corn. The larvae will feed on the foliage and tassels, similar to armyworm, until the ears become available. When larvae are found feeding on younger corn, the damage is accounted for along with any borer or armyworm damage to determine if a spray is warranted. We will be watching our traps closely to keep you informed as the situation changes.

Fall Armyworm: This is usually the last serious corn insect pest to arrive in Maine. The moths must fly in from southern overwintering sites, and tend to lay their eggs on the youngest corn available. When the larvae hatch, they chew large, ragged holes in the leaves, and may bore into developing ears. No fall armyworm moths have been captured yet and no feeding damage has been observed to date.

Other Pests of Note:

Common Armyworm has been found in several fields over the past week. Like fall armyworm, this caterpillar chews large holes in young corn. The larvae are light brown with yellow and black stripes running along the body. This insect is usually only present early in the season and the corn can often outgrow the injury. However, heavy infestations may require control. In general, when these pests cause significant injury in a field, we count the injury along with European corn borer damage. So, if damage from these pests, plus the injury from corn borer exceeds 30% of whorl stage plants or 15% of pre-tassel plants, we would recommend a spray to control them.

Common Stalk Borer This pest can be a problem early in the season, but usually only around the edges of fields. The injury is similar to European corn borer, but the feeding holes are larger. The larvae are purple colored with white stripes. If high numbers of stalk borer are found in pre-tassel stage corn within the field (not just along the edges) include the injury with corn borer to determine if a control is needed.

Do-It-Yourself IPM: To get the most accurate information about the pest situation on your farm you should monitor the fields yourself on a regular basis. Pheromone traps and lures are available that can give you an accurate, early warning of the arrival of all of the major insect pests. Pheromone traps and lures can be purchased from pest management supply companies such as Gempler's in Mt. Horeb, Wisconsin (1-800-382-8473) or Great Lakes IPM in Vestaburg, Michigan (517-268-5693).

To learn more about IPM scouting techniques, insect identification and control thresholds, order the fact sheet Managing Insect Pests of Sweet Corn available from the University of Maine Cooperative Extension. Color pictures are provided to help with insect identification, and a chart with spray thresholds is supplied to post near your sprayer for easy reference. For copies of this free publication contact the Pest Management Office at 1- 800-287-0279.

TARNISHED PLANT BUGS

Tarnished plant bug adults and nymphs are being found in several vegetable crops, and in some fields they are caus-ing significant damage. There are European tarnished plant bugs (Lygus rugulipennis) and American tarnished plant bugs (L. lineolaris), as well as many other species of Lygus bugs. Adults are about 6 mm long (1/4 inch), brown or tan or greenish with darker markings on their wings and back. Nymphs are bright green and progress through 5 molts (instars) from first hatch to the adult stage. They can be mistaken for aphids, but move much faster when disturbed. Overwintered adults lay eggs in spring, depositing eggs in stems and leaf ribs in host plants. These adults and nymphs attack strawberry flowers in May. A new generation of adults (which is what we are seeing now) will produce an-other brood in the late summer, for a total of 2 or possibly 3 generations per year.

Feeding
Adults and nymphs have piercing sucking mouthparts (stylets) which are used to pen-etrate plant tissues and suck up cellular contents. TPB select succulent, nutritious tissues such as new growth or newly forming fruits (just after blos-soming). While feeding, the bugs secrete a toxic substance from their salivary glands which kills cells surrounding the feeding site. Usually the first signs of damage are small brown spots on young leaves. As the tissue grows, healthy tissue expands while dead tissue does not, which results in holes and distorted, malformed leaves, buds or fruit. Ter-minal shoots and flowers may be killed.

Damage
In strawberry, this distorted growth of fruits is known as cat-facing. In celery, feeding on tender stalks produced large, brown colored wilted spots and blacking of joints, know as "black-joint'. In beans, feeding on flowers causes them to drop, and feeding on seeds in young pods causes pitting and blemishing of pods. In tomatoes, eggplants and peppers, feeding may occur on flowers and stems, causing flower drop. Fruits may also be attacked leading to inden-tations, bumps, or yellowing of the flesh where the fruit is "stung" by the piercing mouthparts of nymphs or adults. These could be confused with stink bug damage, but they do not have the white pithy areas beneath the skin that is typical of stick bug damage. It is not common to see this damage, but if the damage occurs it may help to determine the cause. In pepper and in basil, feeding in emerging leaves causes distortion and browning of leaves. In apples, adults feed on fruit buds and cause fruit dimpling and scab-bing, or dropping off (abscission) of the buds.

We have been finding TPB damage in water spinach, which is being grown as a succulent green for Asian markets. TPB feeding occurs in the tiny new leaves in internodes. Holes are punctured in the folded tiny leaves and cells are killed, and as these leaves open up this results in symmetrical holes and distortion of the leaves. Brown scars occur in the internodes. Plants develop more branches in response to dead terminals, which makes them less marketable. Markets want long, single stems with as little branching as possible.

Weeds also Host Bugs
Tarnished plant bugs attack a large variety of crops weeds, flowers, and orchard crops. Weed hosts include wild carrots and other umbelliferous crops, redroot pigweed (and other amaranths), lambsquarters, mustards, shepardspurse, rocket, goldenrod, and mullein. Alfalfa is a favored host, and harvesting alfalfa often stimulates major lygus migrations. Other legume hosts include vetch, lupine, and fava beans.

Management
Whole farm management should include removing sources of infestation outside the crop. Disk or rototill weeds along field borders to reduce weed hosts, or keep them mowed all season. However, disturbing non-crop areas by mowing can encourage movement of TPB into your crop, so it should be avoided at critical periods when the crop is vulnerable. There are natural enemies of TPB, including a parasitic wasp which was released for control of TPB in alfalfa (Peristenus digoneutis). This was released in New Jersey and has spread throughout the northeast, and can cause up to 50% mortality. However, it currently does not reduce the numbers sufficiently to prevent damage in key crops. Most vegetable crops can sustain a small population of TPB without economic injury. We have observed econom-ic damage in water spinach and Thai basil. Unfortunately it is difficult to find insecticides which are labeled for these crops.

(modified from a report by-Ruth Hazzard in the Mass. Veg. Newsletter)

(About the author: Eric is MOFGA’s Technical Services Director, essentially an organic "extension agent". He can be reached at the MOFGA office to answer your questions about farming and gardening. Link to MOFGA Contact Page, or email Eric directly.)