MOFGA Pest Report 2005
26 May

(View List Of All 2005 Pest Reports)

I hope this is the last week that I have to mention wet weather and the problems associated with it. The soil is totally saturated. Greenhouses are full of seedlings waiting for the soil to dry out. Now the problems are being seen in greenhouses because of the lack of sun and cool conditions, such as lots of damping off, yellowing because plants are sitting too long in pots that are too small, leggy plants because of low light level and now fungus gnats.

Fungus Gnats

Good pictures can be seen at:

http://www.daylilies.org/ahs_dictionary/fungus_gnats.html

The eggs hatch in less than a week and the slender, legless maggots with black heads and nearly transparent bodies work their way through the soil. These larvae feed on organic matter in the soil and the fine roots and other plant tissue. The above ground portions of the plants are not damaged, but the plants show a lack of vigor and the leaves turn colors as the nutrition of the plant fades with lack of root function.

The best management for fungus gnats is minimize moisture, both in the crop containers and under benches. Allowing the soil to dry to as great a degree as possible without injury to the plants is effective at killing many of the maggots, but it will not kill all of them.

Because of the lack of sun and high humidity, it has been nearly impossible to have the soil dry out and I am now getting calls about fungus gnats. To monitor for the presence of the larvae place a few peeled raw potato slices about a quarter to half inch thick on the surface of the growing medium for several hours. This will attract the larvae and give you an indication of how extensive the infestation is and whether or not your control measures are working.

If you have a big problem and you think you will have plants in the greenhouse long enough to warrant treatment this year, here are some things that work, but they all take a bit of time and seedlings should be going out soon so you have to decide if it is worth it.

There is a predatory mite for control of fungus gnats called Hypoaspis miles. This mite is a scavenger and will survive in the absence of fungus gnats and will consume larvae as they appear.

There are beneficial nematodes that prevent outbreaks of fungus gnats. They are sold under the name ScanMask.

There is a Bt strain (Bacillus thuringiensis var. israelensis) that is sold under the brand name Gnatrol. It is used as a soil drench to control an outbreak of fungus larvae.

All three of these can be bought from IPM Laboratories (315 497 2063) and probably from the supply houses I mentioned in the past for beneficial nematodes.

All three of these biological controls act on the larvae, which is causing the damage, but the adults will fly around for a while longer. The Bt treatment will have to be repeated three times to catch later egg hatching. The nematodes and mites will survive long enough in the soil from a single application to catch them all.

Best would be to get some sun.

STRAWBERRY IPM NEWSLETTER

University of Maine Cooperative Extension

NOTE: This is the Strawberry IPM Newsletter produce by David Handley, Maine's small fruit specialist. I will periodically take things from this and reprint them in my Pest Report, but today I have sent you all of his Newsletter that is relevant to organic growers. If you would like to receive the Newsletter directly from Dave in its entirety, see the instructions on where to get it in the first paragraph.

No. 1 May 24, 2005
2005 STRAWBERRY PEST MANAGEMENT SEASON BEGINS
Hard Winter + Wet Spring = Tough Start to the Season

Due to the very poor weather, we have only had one day of reasonable scouting, so we don't yet have a detailed situation report. However, it is time to review the pest management strategies for the season, and let you know how things will progress over the coming weeks. We will be scouting strawberry fields at several volunteer farms for major insect pests, including locations in North Berwick, Wells, Cape Elizabeth, Poland Spring, New Gloucester, Dresden, Litchfield, Wayne, and Farmington, and will be reporting our findings through this newsletter on a weekly basis until harvest time. You can also get quick access to this information through the Pest Management web page on the Internet at http://pmo.umext.maine.edu. If you would prefer to receive this message via e-mail, please give us a call at 933-2100 or send an e-mail message to: dhandley@umext.maine.edu.

The best way to manage strawberry pests is to scout your own fields regularly and often. You should be able to identify the major pests and their damage, and be able to determine if controls measures are necessary. To properly scout your fields you may want a copy of the Strawberry Production Guide for the Northeast, Midwest and Eastern Canada. This contains detailed information on strawberry pest identification and monitoring, and also provides information on all other aspects of strawberry production, including varieties, planting systems, nutrition, marketing and more. It may be purchased for $48.00 per copy from the University of Maine Cooperative Extension at Highmoor Farm, P.O. Box 179, Monmouth, ME 04259-0179. Checks should be made payable to Cooperative Extension.

Situation: A very cold start to the winter last year, following a warm fall and before a good snow cover arrived appears to have left many fields with some winter injury (see article below). A brief warm spell early in the season got plant growth off to a good start, but extended cool and very wet weather since has slowed plant growth considerably. By our estimates, Highmoor farm is nearly two weeks behind average plant development for this time of year, based on degree-day modeling. Fields in southern Maine are not yet in bloom, with the exception of some plants that were under rowcovers this spring. Frost has been an issue for these fields, with temperatures dipping into the low 20's just over a week ago. This cold weather has also slowed insect development, and we have not yet seen any evidence of tarnished plant bug or clipper activity, and only a few spider mites.

Strawberry bud weevil or "clipper" should soon be active in strawberry fields as flower buds are emerging from the crown. While we have not yet found significant clipper activity, these insects are likely to be active in any fields where flower buds are present, once the weather improves. The clipper is a small weevil, which girdles strawberry flower buds causing them to dry up and fall off the flower stalk. The damage should be scouted for by counting the number of clipped buds in two feet of row length at five different locations in a field. If the average number of clipped buds per two-foot sample exceeds 1.2, or if one or more live clippers are found, control measures are recommended. Damage is usually first noticed at the edges of the field. Border sprays may be effective in keeping this insect from becoming a problem throughout the field. Fields with a history of clipper problems can be expected to exceed threshold nearly every year.

Tarnished plant bugs should be starting to become active. We have seen a few adults this spring, but no nymphs yet. Adult plant bugs should be laying eggs, but the cool yet weather may be taking its toll. Nonetheless, we expect to start seeing nymphs soon. The nymphs are small, active, yellow-green insects. It is important to scout for the nymphs regularly, as they can show up quickly in warm weather. Tarnished plant bugs feed on the open strawberry flowers, causing the berries to have seedy ends. To scout for this insect shake 30 flower clusters (six clusters in five different locations) over a plate. If four or more of the clusters out of the 30 sampled have any nymphs, control measures should be taken. Be on the alert and scout your fields now!

Twospotted spider mites have been found in fields this week, but population were quite sparse. Spider mites will reproduce rapidly when warmer weather arrives, so it is important to scout for them regularly. Spider mites feed on the undersides of strawberry leaves, rasping the plant tissue and sucking the sap. Infested leaves will develop yellow flecking and a bronzed appearance. The plants become weakened and stunted. Fields that have had excessive nitrogen fertilizer and/or rowcovers tend to be most susceptible to mite injury. To scout for mites collect 60 leaves from various locations in the field, and examine the undersides for the presence of mites. Mites are very small - you may need a hand lens to see them. Predatory mites, such as Amblyseius fallacis, can provide good control of two spotted spider mites when they are released at a rate of about 10,000 mites per acre. Predator mite releases should only be made after a spider mite infestation has been found in the field. Releasing predators into a clean field will often result in them dying, due to a lack of food.

Diseases: Many strawberry plantings will soon be coming into the bloom stage. Bloom is a critical time to protect the fruit against gray mold, especially when conditions have been damp. Two to three sprays of fungicide during bloom are typically required to provide good protection against this disease. If you tank mix insecticides and fungicides, avoid spraying when bees are active. Leather rot and leaf spot are also become an issue this season because of the prevalence of water in the fields, and may require different materials to provide good control.

Gray Mold Gains Foothold in Strawberries at Bloom
Annemiek Schilder, Michigan State University

Gray mold, caused by the fungus Botrytis cinerea, is one of the most important fruit rot diseases affecting strawberries. Wet weather and moderate temperatures are conducive to development of this disease. Typical symptoms include a brown discoloration of the fruit and the presence of a gray fuzzy mold, which can rapidly develop and spread to neighboring healthy berries. Even if berries look perfectly healthy at harvest, they can start to show rot within several days in cold storage or the refrigerator.

Botrytis cinerea overwinters on old leaves and plant debris and can sporulate profusely on dead plant material. The spores easily become airborne and are usually plentiful in strawberry fields. In strawberries, primary infections take place almost exclusively through the flowers. This is why gray mold control efforts should be focused on the bloom period. If the bloom period is dry and/or good fungicide coverage is maintained, incidence of gray mold at harvest will be low. However, if infections occur at bloom, they remain dormant until the berries start to ripen. As gray mold develops on ripening berries, the emphasis has to be on preventing new infections of the surrounding berries, which become more susceptible as they ripen. Infected berries can easily infect other berries that touch them. Sometimes whole clusters are covered with the gray spore masses. Where possible, remove sporulating berries from the field and destroy them to limit inoculum availability. During picking, avoid handling infected berries, since spores can be transferred on hands to healthy berries. Timely harvesting and rapid post-harvest cooling may also help to reduce losses to Botrytis gray mold.

Leather rot (Phytopthora cactorum) is best controlled by growing strawberries in well-drained soil and by applying straw mulch between the rows to prevent the berries from touching the soil (where the fungus resides) and prevent soil from splashing up onto the berries.

Most other fruit rots, including anthracnose, tend infect the berries somewhat later in the season, i.e., during the green fruit or ripening stage. Anthracnose fruit rot is favored by warm, humid conditions and can spread rapidly during rains or frequent irrigation. In cool seasons, it tends to appear closer harvest or may not show up at all. Anthracnose fruit rot can be identified by black sunken lesions with wet, orange (and sometimes gray) spore masses in them. The anthracnose fungus is able to multiply on the leaves without visible symptoms, which may explain its sometimes widespread and sudden appearance in fields.

Root Weevil Management
>From info supplied by Richard Cowles, CT Agricultural Experiment. Station; Peter Shearer, Rutgers Cooperative Extension; and others

Despite the hard winter, we have observed some plantings of strawberries infested with the grubs of black vine weevil and strawberry root weevil this spring. It is not too late to put on an application of nematodes to control the grubs (optimal timing is about mid-May). Two species of nematodes appear to offer the best control of root weevil grubs. Heterorhabditis bacteriophora (Hb) appears to be the best candidate for control of root weevils when the soil temperature is above 60 degrees ('J-3 Max Hb' from The Green Spot; 'GrubStake HB' from Integrated Biocontrol Systems; 'Larvanem' from Koppert Biologicals). Beneficial nematodes can also be applied in late summer (August 15 - September 1), and in that case, Steinernema feltiae ('Nemasys' from Griffin Greenhouse Supply, 'Gnat Not' from Integrated Biological Control Systems, 'Entonem' from Koppert Biological) should be considered in northern locations since it tolerates cooler soil temperatures and completes its life cycle quickly. Once the grubs begin to pupate (usually early June) nematodes should not be applied, because they do not attack the adult (beetle) stage. . Neem-based products containing azadiractin (such as Aza-Direct) may be acceptable for organic production, and while neem will not kill the adults it can disrupt egg-laying if applied at high rates at least twice.

Nematodes are living organisms and they can be killed if they are misapplied. Order nematodes ahead of time and be ready to apply them through a sprayer or irrigation soon after they arrive, refrigerating if delay is necessary. Do not apply nematodes using a sprayer with a piston pump. Use clean equipment, removing all screens finer than 50-mesh. Apply nematodes in early morning or evening in a high volume of water to already moist soil, pre-irrigating if needed. Apply another ¼ inch of irrigation after application to wash them onto and into the soil. Although references suggest rates of several billion nematodes per acre, I found researchers and suppliers recommended 250 (if banded in the row) to 500 million per acre, at a cost of about $100 to 200 acre depending on volume and source. Ironically, nematodes probably work best in the worst weevil-infested fields. High populations of weevil larvae allow explosive growth in nematode populations, while low populations of larvae may not permit efficient nematode reproduction. Strawberry plants can recover their vigor remarkably well if crown feeding has not occurred and diseases haven't taken over the roots.

Root weevils cannot fly, so they infest new plantings by wandering into fields from surrounding weedy and woodland vegetation, or in large numbers from recently plowed, infested strawberry plantings. Even plantings several hundred feet away can become generally infested as a result of mass migration from plowed fields. A good rotation program with substantial distance between strawberry fields can help to manage root weevils. Also, when turning under old, infested strawberry plantings, it is critical to leave a row or two at the perimeter of the field as a trap crop to protect other plantings. Adult weevils will be intercepted in these rows before they leave the field and thus lay their eggs where the larvae will not do any damage. At the end of the season the trap rows should be turned under prior to planting winter rye. Do not spray the trap rows as this may repel weevils and result in more migration to other fields.

Some Beneficial Nematode Suppliers:
The Green Spot: 603-942-8925 or www.shopgreenmethods.com
Griffin Greenhouse Supplies: 978-851-4346 or www.griffins.com
Integrated Biological Control Systems: 888-793-4227 or www.goodbug-shop.com
Koppert Biologicals: 800-928-8827 or www.koppert.com

[Note: I provided contact info for some other suppliers of beneficial nematodes in the cutworm discussion in the May 9, 2005 issue of the Pest Report]

Red Stele Root Rot a Potential Threat

The heavy rains this spring led to saturated soils and ideal conditions for red stele root rot. Don't assume that plants dying in the field are the result of winter injury unless you have first checked for symptoms of red stele. To diagnose red stele, pull up a few plants that look weak, i.e. have small leaves, scrape the roots of these plants to see if the center of the root, known as the stele, is a rusty red in color, instead of the normal white. The red color would indicate an infection. Red stele is cause by Phytophthora fragariae, a soil borne fungus that infects the roots when soils are saturated with temperatures around 50*. The fungus grows into the roots and blocks the vascular system causing the plants to become weak, stunted and eventually die. Sypmtpoms are most evident in the spring, and can be mistaken for winter injury. Many varieties have some level of resistance to the disease, but the most effective management strategy is to plant only into well-drained soils.

Winter Injury in Strawberries?

We have found varying amounts of winter injury in the fields we have visited so far. Despite the fact that strawberries are an important and successful crop here in Maine, they are not particularly hardy plants. Most varieties will experience cold injury at temperatures of 10° to 15°F, which are not uncommon during a typical Maine winter. However, the combination of mulch and snow cover usually provides adequate protection during the winter, keeping the temperature around the plants within tolerable limits, even when air temperatures drop well below injurious levels. However, if mulch coverage is poor, due to removal by wind, animals or other factors, and/or there is a lack of adequate snow cover during the coldest periods of the winter, then cold temperature injury could be a problem.

To assess suspected winter injury in a strawberry planting, plants can be sampled throughout a field, noting different varieties and landscape features, such as elevation, lack of mulch coverage, etc. Examine the crowns and roots for color. Beneath the protective brown or black dead layer, there should be healthy, firm, white tissue. Slice the crowns lengthwise to examine the interior tissue. Brown discoloration at the base of the crown indicates a mild but significant level of injury. The degree of injury increases as the amount of browning extends toward the top of the crown and gets darker in color. If the tissue is killed all the way to the top of the crown, including the leaf and flower buds, plant death is very likely, but this rare. Strawberry plants usually survive milder injury, but even slight browning in the crowns often leads to reduced plant vigor and yield.

You can help alleviate the symptoms of winter-injured plants by applying a light dose of nitrogen to the plants. This can help stimulate new root growth and leaves, improving the plants ability to support larger fruit and thus improving yield. Approximately fifteen to twenty pounds of actual nitrogen applied in the spring as growth starts can stimulate new growth, without causing excessive foliage growth that can encourage mites and fruit rot.

Twilight Meeting - Mark Your Calendars Now!
The University of Maine Cooperative Extension and the Maine Vegetable & Small Fruit Growers Association will hold a Twilight meeting in Fryeburg at Weston's Farm on Wednesday evening, June 15th at 5 p.m. George, Laurie and John Weston will host all interested vegetable and berry growers at their place on 48 River Street in Fryeburg. We will tour the fields of strawberries and vegetable crops and discuss the production and marketing techniques employed at this historic farm. More details to follow.

Sincerely,

David T. Handley
Vegetable & Small Fruit Specialist

Highmoor Farm Pest Management
P.O. Box 179 491 College Ave
Monmouth, ME 04259 Orono, ME 04473
(207) 933-2100 1-800-287-0279

If you are a person with a disability and need any accommodations to participate in the programs mentioned in this newsletter please call 207-933-2100 to discuss your needs.

Maine Cooperative Extension, the Land Grant University of the state of Maine and the U.S. Department of Agriculture Cooperating. Cooperative Extension and other agencies of the U.S.D.A. provide equal opportunities in programs and employment. A Member of the University of Maine System.

BRASSICA PESTS

Flea beetles continue to be active. New plantings should be covered carefully with row cover, or be prepared to use insecticides. Rotate far from last fall's Brassica crops if possible. -(adapted from Vegetable Notes from U Mass-R. Hazzard)

PERIMETER TRAP CROPPING Q&A

NOTE: Many of you were at the New England Vegetable and Berry Conference in 2003 and heard Jude Boucher speak on Perimeter Trap cropping and gave me very good reports on this research. Here are some Q&A for you all. If you missed this, don't miss the 2005 Conference (see http://www.nevbc.org/). And, Jude is going to speak at MOFGA's Farmer to Farmer Conference this year (November 4-6)

Q: What if I only have small plantings of mixed winter squash? Can I still use PTC?
A: Absolutely. All you really need to do is separate out the maxima species in your mixed planting and place them around the edges. If the outer one or two rows are squash from the Cucurbita maxima group, such as buttercup or blue hubbard, as well as the first and last couple of plants in each row, you will in effect have created a PTC border. This is an effective way to use a PTC system in a small mixed planting. For a list of winter squash and pumpkins in the Maxima group, please see the list below.

Q: Do I have to use blue hubbard squash for a trap crop?
A: While Blue Hubbard works very well as a trap crop, it is by no means the only thing that will work. We have found that most winter squash and pumpkins in the C. maxima group, such as buttercup squash, giant pumpkins, and Cinderella pumpkins, make excellent trap crops. You could even plant a mix of these species around your crop, so as not to have too much of any one thing. The one thing that you want to make sure of is that you don't plant a trap crop that is particularly susceptible to wilt, like Turk's Turban.

Q: What if I don't have a market for Blue Hubbard squash, or any of the other C. maximas you are recommending?
A: If you can't or don't want to sell your trap crop, you can simply till in the trap crop once the main crop is far enough along to be able to withstand any further beetle pressure. Generally, once the main crop is getting ready to vine, the worst of the danger is over. At that point you can just till in the trap crop and let the main crop spread into the perimeter.

Q: Can I use PTC for anything other than Butternut squash?
A: At UMass and UConn we have found that PTC systems have worked well in winter squash, pumpkins, summer squash and cucumbers. The system may also have potential in summer cantaloupe, though we haven't evaluated those crops as of yet. Zucchini is quite attractive, and should be watched closely as a main crop. -(from Vegetable Notes, UMass-Andy Cavanagh, UMass Extensions)

(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.)