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 MOFGA's 2006 Pest Reports - Compiled by Eric Sideman, PhD Minimize

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STUNTED LITTLE YELLOW PLANTS, WILL THEY RECOVER? It depends. The weeks of rain have set farmers back but also have set the crops back too. There are two major reasons. The first is that the roots of nearly all species of plants must have oxygen available to them and when the soil becomes waterlogged all of the air spaces are filled. Roots stop absorbing nutrients, especially nitrogen. If it stays wet long enough the roots die.

The second cause of the hurt plants has to do with the way nitrogen behaves in the soil. Nitrogen can be found in soil in many forms such as the gas nitrogen, as part of the proteins in organic matter and as ions such as nitrate, nitrite and ammonium. Most plants can only pick up the nitrogen when it is in the nitrate form and some when it is in the ammonium form. In soil that has air and moisture but not too much, nitrogen cycles around these different forms by biological activity and some is always passing through the nitrate form and is available to crops. When the soil is too dry, too cold or too wet the cycling stops or can even change direction so the nitrogen is lost from the soil either by leaching or by reverting to a gas form and goes out into the atmosphere. This may happen only in portions of fields where water puddles.

When the rains of May and early June came some of the nitrate was lost by simple leaching. When the soil became waterlogged and anaerobic the nitrate reverted to nitrogen gas and was lost. If most of your nitrogen was in the nitrate form at this time, it is gone. Folks who use chemical fertilizers will probably have to reapply it. The nitrogen that was in organic forms such as seed meals, fish meal, compost and livestock manure probably will still have much of the nitrogen left because the soil became cold and anaerobic before the bacteria converted the organic nitrogen to nitrate. Farmers just have to wait for the air spaces to reappear in the soil and the bacteria to get to work. Of course, this should have happened in April and so it may be wise to supplement your crops with a bit of available nitrogen while this is happening now in the middle of June. And, non of this will help those crops whose roots died.

Spring in New England is nothing but fun.

MANAGING COLORADO POTATO BEETLE: Colorado potato beetles (CPB) are moving into potato and eggplant crops, and will soon be laying eggs. Some adult beetles spent the winter in last year's potato fields, but most moved into the woods and brushy borders next to these fields, where they burrowed into the soil up to a depth of 12 inches. In spring the beetles have to regrow  their flight muscles before they are able to fly. At first they search for food plants by walking from the field edges. This is why the edge of non-rotated crops are attacked first. If beetles do not find host plants via walking they will fly  some distance in search of food. Once host plants are found adults begin to feed and lay  eggs. The beetles will have mated the previous fall or late summer; hence they have no need to mate in the spring to produce viable eggs. However, they do continue to mate in  spring. The bright yellow eggs are laid in clumps that average 30-35 eggs, generally on the undersides of leaves.

Crop Rotation. The single most important tactic for CPB management is to rotate potatoes or eggplant to a field that is at least 200 yards from the previous year's fields.  Barriers such as roads, rivers, woodlands, and fields with other crops are helpful. Rotated fields tend to be colonized 1-4 weeks later in the season. Also, the total population of  adult beetles is lower, producing fewer larvae to control. Now is the time to scout for adults, eggs and egg hatch.
Walk your fields and look for CPB adults and eggs. The economic threshold for adult beetles in potato is 1 beetle per 2 plants (or per 2 stalks, in midseason). Eggplant  seedlings have a low tolerance to damage. Look on the undersides of leaves for the orange-yellow egg masses. The fresher the eggs, the brighter orange the eggs will appear. Eggs hatch in 7-10 days, depending on temperature. If you want to know when the earliest eggs are hatching, you can flag the earliest egg masses you find with bright tape or flags, and then keep an eye on the hatch. Larvae go through four stages before they drop to the soil and pupate. In the first stage, the larvae are about the same  size as the eggs and in the second stage they are about an eighth of an inch long. As the larvae get bigger, they do more feeding. The fourth, or largest, stage does 85% of the  feeding damage. It's a good idea to prevent beetles from ever reaching the fourth instar!  After larvae complete their growth, they drop to the ground and burrow into the ground to pupate. Ten days later the next generation of adults emerge and feed. If they emerge before August 1, they will lay more eggs. After August 1, they feed and head to overwintering sites.

Spray timing and thresholds: To prevent resistance the best strategy is to alternate among classes of insecticides in each generation, and throughout the season. An example would be to use a material such as Spinosad (Entrust), which controls adults and larvae for the first spray, followed by a Bt (Novodor) to kill emerging young larvae. BUT, at this time there is no Bt formulation approved for use in organic systems. NOVODOR IS NOT APPROVED FOR ORGANIC PRODUCTION BECAUSE OF INERT INGREDIENTS. VALENT, THE COMPANY THAT MANUFACTURES IT, AT ONE TIME SAID THEY WOULD REFORMULATE IT TO MEET ORGANIC STANDARDS, BUT SEEM TO HAVE CHANGED THEIR MIND. GIVE THEM A CALL AND TELL THEM HOW IMPORTANT IT IS TO ORGANIC GROWERS (1 800 323 9597).

If you are not organic and are using Bt (Novodor), you want to make the first application when 20- 30% of the eggs have hatched. If you are using spinosad (Entrust is the organic formulation) you can wait until more larvae have hatched, when the oldest larvae reach the third instar, when they are about 1/3 inch long. Applications made at this time with Entrust will kill all the larvae that have hatched up to this point. The threshold for small larvae is 4 per plant; for large larvae, 1.5 per plant (or per stalk in midseason), based on a count of 50 plants or stalks. Thresholds established in the Northeast for eggplants from seedling to fruiting stage include: 15 CPB per 10 plants (Rutgers) or 2 small/1 large larvae per plant (<6 inches) or 4 small larvae /2 large per plant (>6 inches) (Cornell). In eggplant, in addition to defoliation, beetles sometimes clip the stems of flowers or flower buds. This directly reduces fruit formation and marketable yield. On the other hand, potatoes can tolerate 20% defoliation without reduction in yield (or even more, later in the season and depending on cultivar).

Perimeter treatments or perimeter trap cropping can be applied to potato. One approach is to plant a barrier crop between overwintering sites and this year's crop and get  it in earlier than the main crop; then control early-arriving beetles with a foliar insecticide. In eggplant or tomato, the perimeter border can be an Italian eggplant type, which is more attractive to both CPB and flea beetles. Treat only the border, as soon as beetles arrive.

Late planting: Another strategy for beating the beetle is to plant late. CPB adults that do not find food leave the field in search of greener pastures. Planting after mid- June, using a short  season variety, often avoids CPB damage and eliminates the need for controls.  -(modified from an article in UMASS Vegetable Notes by Ruth Hazzard. R Hazzard says thanks to sources including: D Ferro (Umass Amherst), J. Mishanec (CornellUniversity), J Boucher (Univ. of Connecticut).   Where trade names or commercial products are used, no company  or product endorsement is implied or intended. Always  read the label before using any pesticide. The label is the legal  document for product use. Disregard any information in this  newsletter if it is in con*ict with the label.

RASPBERRY WINTER INJURY:  Even though red raspberries are the hardiest of the bramble fruits, we are seeing a lot of what appears to be winter injury on overwintered floricanes of summer-fruiting raspberries throughout the state. Fall-bearing cultivars whose canes are mowed every spring are not sensitive to winter injury, and aren't showing damage.

What does winter injury look like? The most common symptom of winter injury is dead canes or dead tips on overwintered canes. In some cases, canes may leaf out later than expected, or not at all. You may also see dry, cracked areas along the length of dead or damaged canes. Milder winter injury can also affect vascular tissue so that canes can leaf out and appear healthy, but when temperatures warm up and canes start to grow rapidly, the damaged vascular tissue cannot supply laterals with water, so the laterals collapse.

But I thought we had a pretty mild winter… Winter injury can be caused by very cold temperatures (-20C), but can occur even when temperatures are not that low. Last winter was mild, but we did experience some of the other conditions that make winter injury more likely:
  • A very warm wet late fall. In most parts of NH, our first fall frost happened late - the end of October. Until then,  perennial plants just kept growing, and did not have time to transition slowly and gracefully into dormancy. The rapid  transition to winter occurred before plants were fully dormant and tissue was more tender than normal.
  • No snow cover. Winter injury is caused by wind desiccation as well as by very cold temperatures. Snow cover does doubleduty,  insulating canes from lower temperatures and protecting them from wind and drying out. Very little snow during  the winter meant that canes were more exposed than normal.
  • Large temperature fluctuations. Although this may not have affected raspberries as much as other perennials, warm spells  followed by sudden drops in temperature can injure plants that have started to break dormancy during the warmth. We  had a couple of large (>50 degrees) sudden drops in temperature in January and February that could have played a role.
What to do? Now that healthy canes have leafed out completely, prune back and remove dead winter-killed tissue  and canes. In future years, the following precautions can help to prevent winter injury:

  • Choose a site well-sheltered from prevailing winds.
  • Grow hardy varieties (Boyne, Killarney, Nova are very hardy; Titan, Taylor, K81-6, and Lauren are less so).
  • Do not over-fertilize. Mature plantings usually require about 50-60 lbs actual nitrogen per acre per year.
  • Do not trim new canes (primocanes) back after July 1.
  • It's also important to minimize other stresses. Damage by voles, soil-borne diseases like Phytophthora, and cane  diseases like anthracnose and spur blight all weaken canes and predispose berries to winter injury.
[adapted from the New Hampshire Vegetable and Berry Newsletter by Becky Grube and George Hamilton]

Steve Johnson from Umaine Extension sent this interesting note out.

We are trying a new approach to late blight risk. The table below is a compilation of practices and events that can put a field at risk for late blight. THESE RISK RATINGS ARE NOT SEVERITY VALUES. RISK RATINGS ARE AN INDICATOR OF THE POTENTIAL THREAT FOR LATE BLIGHT.

I've summarized some current risk issues:

All fields have accumulated 1 risk rating  
Most fields have accumulated an additional 4 risk ratings (total of 5)
Some fields have accumulated yet an additional 1 risk rating (total of 6)  
+ 1 each  
LB present in Region last season    All fields included
LB present in Area last season    Most fields included
LB present on Farm last season    Some fields included
≥ 18 Severity Values met    Most fields included

+ 1 per day per event
Weather forced longer spray interval than recommended    Most fields included (or will be by Monday June 12)
SW field capacity > 0.95 %    Most fields included

Some fields may have additional risk ratings based on the below practices or events.  
+ 1 each  
Cull piles in area       
Seed was cut and held for ≥ 3 days  
Seed was not treated with MZ  
OK ≤ 3  

We are in a risky situation with the predicted upcoming weather. Friday morning we had accumulated 20 hours of infection conditions. By Saturday morning that is expected to 44 hours and by Sunday morning, 68 hours. That alone will accumulate more than 18 severity values. As soon as possible, coverage need to be put on emerged plants. Those that have fields in the "some fields" category or those that have any of the additional risk included here:
+ 1 each  
Cull piles in area       
Seed was cut and held for ≥ 3 days  
Seed was not treated with MZ  
should consider the addition of cymoxanil to the tank mix. At this point, timing is more critical that the rate of material.

Keep current by calling the hotline (760-9ipm) or visiting the website:                                           

and clicking on the Pest Alert link.

The complete table for risk ratings (Late Blight Risk Table.pdf) appears on the Pest Alert page  

Steven B. Johnson, Ph.D.                     
Crops Specialist and Extension Professor                            
University of Maine Cooperative Extension    
P.O. Box 727, Houlton Road                   
Presque Isle, Maine 04769                    
1-207-764-3361 VOICE        
1-207-764-3362 FAX          

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