Apple Pest Report:
Saturday,
July 24, 2004
Vol. 12 No. 6
Scab
Scab levels in monitored blocks have come down. If you are still finding 5 or more leaves with apparently active lesions per 100 shoots, then a good scab fungicide such as captan, Flint, or Sovran should be applied every 10-14 days until the scab level recedes.
Unfortunately, even though there is a captan formulation now labeled with a 24 hour Restricted Entry Interval, it seems that product will not be available in Maine this season, so only the 96 hour REI formulations are available.
Flyspeck and other 'Summer diseases'
The number of leaf wetness hours accumulating per day in July is running about 35% above normal at Highmoor Farm. This accelerates the development of flyspeck colonies. Last year, humid conditions in early August combined with heavy rain on Sept. 4, 2003 followed by more wet weather all combined to produce an extra generation for flyspeck. The number of colonies can increase with each generation. Of course there is no way of knowing what will happen in August and September, so far this year we are again seeing conditions more favorable than "normal" for flyspeck development. The risk of infection increases at the end of July as second generation flyspeck colonies become developed enough to produce spores to start third generation infections.
Sovran or Flint are the best fungicides to prevent flyspeck, and a full dose application will provide protection for about 21 days or 3.5 inches of rain. Sovran and Flint can also reach back to stop growth of infections that have had less than 100 leaf wetness hours since starting. Full dose captan, or Topsin M + half dose captan will protect for about 21 days or 2.5 inches of rain.
The flyspeck fungicide respray guidelines for the Orchard Radar sites can help you keep track of the number of leaf wetness hours since your previous fungicide application (e.g. Monmouth, Sanford, Gorham, Old Town)
Insects and Mites
Apple maggot flies have quickly exceed threshold at Highmoor Farm. If you don't have insecticide protection in place, unless you have your own trap catches to indicate otherwise, apples should be protected from apple maggot egglaying. Based on last year's experience when, with similar weather, apple maggot trap captures started high and never let up, we could be in for another high apple maggot population year.
European red mites (ERM) are more present this year than in the past few years, though levels in monitored blocks are still below threshold. The cool wet weather of late should help to keep them in check. By late July, ERM females start to lay an increasing percentage of their eggs as overwintering eggs that will not hatch until next spring. The threshold until August 15 is an average of 5 living hatched mites per leaf (don't count dead mites or unhatched eggs), or if more than 73% of middle aged leaves have mites present.
Leafminers: The optimum date to check for second generation sap-feeding leafminer mines is now in Sanford, July 26 in Gorham, and August 1 in Monmouth and Old Town. A reasonable all purpose threshold is an average of 1 mine per leaf, but you might want to nudge that threshold up or down depending on tree condition and crop load.
Codling moth are currently between first and second generation egg hatches.
Borers: Backyard orchardists who aren't spraying insecticide for other pests need to either spray trunks, have physical barriers in place, or plan for borer checking in September. Now is the time for peak roundheaded apple tree borer egglaying and egg hatch is underway.
Weeds
Now that we are past the midpoint of the growing season, it becomes hazardous to apply systemic herbicide such as glyphosate (Roundup) around apple trees, especially trees with root suckers. There has been plenty of winter damage visible this year, the last thing trees need this fall is another stress.
(Dave Rosenberger, Plant Pathology, Highland; and Mike Fargione, CCE, Hudson Valley Regional Fruit Program)
Over the past five years, we have noted with increasing frequency a kind of trunk injury on apples trees that does not fit the description of any known disease. The injury usually occurs at or near ground level and extends 2-8 inches up the trunk from the graft union. Frequently the injury is confined to one side of the trunk, but in some orchards large numbers of trees are killed after trees become girdled. Bark on roots below the soil line and on the trunk above the cankered area remains healthy. The canker margin is usually rather distinct. In some orchards, cankers are most prevalent on the southwest side of trees, suggesting that winter injury may be involved. However, in other orchards, the injury may be more prevalent on the northern side of the trees. In eastern New York, tree losses from this trunk canker are becoming more common than tree losses from fire blight.
Most affected orchards have the following characteristics:
o The orchards are well-managed with a very clean herbicide strip.
o Trees affected are generally more than five years old with trunks at least three inches in diameter.
o Severity of damage is often variety-dependent, with especially severe injury noted on Cortland and Macoun trees.
o Affected orchards have received glyphosate (Roundup or generic equivalents) at least once per year.
At this point, we are just initiating research to determine the causes of this potentially lethal trunk canker. However, we are sharing our hypotheses at this time in hopes of minimizing further damage. We also encourage observers to contact us with other ideas, observations, and information.
Hypotheses for explaining herbicide-induced trunk cankers:
1. The trunk cankers result from hitting the lower part of the tree trunks with glyphosate sprays.
2. Stress within the glyphosate-sprayed bark may enable the white rot fungus, Botryosphaeria dothidea, to invade and kill the bark.
3. The glyphosate/B. dothidea interaction may be more lethal in trees that are under water stress when the glyphosate is applied as compared with non-stressed trees.
4. Cankers may not become apparent until several years after the injury that allowed canker initiation. Therefore, eastern NY growers noting cankers for the first time this summer may be seeing results of herbicide injury that occurred during the July-August drought of 2002.
Observational support for these hypotheses:
The patterns of injury on the trunks is often consistent with the exposure pattern that would be expected from an herbicide sprayer where the boom is adjusted to provide overlapping coverage in the line directly between trees within the row. The injury has been observed in orchards where only glyphosate and gramoxone are applied, so we can rule out residual herbicides as a potential cause. Gramoxone has a longer history of usage than glyphosate, and the trunk canker problem emerged relatively recently during the same time frame during which we suspect that orchard use of glyphosate was increasing. The extremely clean herbicide strips in many of the affected orchards suggest late summer applications of glyphosate are common in the affected blocks.
B. dothidea is endemic in most older apple orchards where it commonly occurs in superficial cankers that cause little damage to the tree. However, B. dothidea can become aggressively pathogenic in drought stressed trees. When that happens, necrosis can extend into the inner bark. Thus, B. dothidea is commonly present in older apple trees but can cause serious damage only when trees encounter stress conditions. Perhaps glyphosate alone can cause the injury that we are seeing, but we suspect that in many cases glyphosate and B. dothidea are acting together.
Management implications:
Drastic changes in ground cover management are not warranted at this time because we still have no experimental evidence that glyphosate injury is at the root of the problem. However, if our hypotheses are correct, then the following precautions are worth considering:
1. Glyphosate applications made after July 1st may be more likely to cause injury than those made during May and June, because trees are more likely to be under stress conditions during summer and fall. Gramoxone may be a safer alternative for summer and fall sprays.
2. If glyphosate is applied during late summer or fall, the lowest effective rate of glyphosate should be used, contact with the tree trunks should be minimized, and sprays should not be applied during periods when trees are likely to be water stressed (i.e., during drought periods or on very hot days).
3. Read glyphosate labels carefully! Many different formulations are currently available, so anyone using 10-yr-old notes when adding glyphosate to their spray tank may be drastically overdosing their trees.
4. Whether using glyphosate or gramoxone, always include a drift inhibitor in the spray tank to minimize the potential for unwanted drift of small spray droplets.
5. Glyphosate should never be applied in orchards using controlled droplet applicators (CDA sprayers) because these applicators by definition generate small droplets that are prone to drift.
In summary, caution is advised when applying contact herbicides during summer or fall. Everything possible should be done to avoid contacting trunks with the herbicide sprays. Finally, we emphasize that the relationships between trunk cankers and herbicide injury or infection by B. dothidea remain to be proven. We will appreciate input from anyone who can contribute further information on occurrences and causes of the trunk canker problem in apples.
Other stuff
1) Highmoor Farm Summer Tour
The Highmoor Farm Summer Tour is July 28th. In the morning will be tours of the research plots and in the afternoon will be our guest speakers.
8:30 AM – 9:00 AM
Registration
There will be a registration fee of $15.00 to cover the cost of lunch and the afternoon program.
Coffee and donuts provided by UAP
9:00 AM – 11:30 AM
Concurrent Tours:
Apple Tour
Small Fruit and Vegetable Tour
The Apple Tour
with Renae Moran and Glen Koehler
First, we visit the new Honeycrisp planting, now in its third year,
for a look at winter survival. Glen will talk about a research
demonstration underway for plum curculio and apple maggot management,
plus a few words on scab scouting and the laminated pest threshold-photo
ID cards. Then we
visit the stone fruit planting for a demo in peach, plum and cherry tree
training. Last, we will look winter injury in a rootstock trial. One
pesticide recertification credit is available for attending the tour.
Vegetable & Small Fruit Tour
Mark Hutton, Vegetable Specialist
David Handley, Small Fruit & Vegetable Specialist
Mark Hutchinson,
Extension EducatorGrowers will tour variety trials of onions, tomatoes, peppers and pumpkins, and experiments with reflective mulches, biodegradable mulches and zone tillage. There will also be a demonstration of pre-sidedress nitrogen testing for sweet corn, and a look at our new high tunnels for extending the harvest season.
11:30 PM – 12:30 PM Lunch
BBQ chicken, beef or pork sandwiches, beans, salads, soft drinks and dessert.
12:30 PM – 1:00 PM
Business Meetings:
Maine State Pomological Society
Maine Vegetable & Small Fruit Growers Association
1:00 PM – 1:30 PM
Adam Thompson, The Dirigo Health Plan for small businesses
1:30 PM – 3:30 PM
Charlie Touchette, North American Farmers’ Direct Marketing Association
"Agritourism Ventures that Increase Family Farm Profitability"
"Consumer Trends: the Answers to Why Farm Direct Marketing Works"
"Merchandising and Promotions: Going Beyond Offering Products for Sale"
3:30 PM Adjourn
Directions. Highmoor Farm is located on Route 202 in Monmouth, Maine.
From the North: Take Exit 109b off I 95 in Augusta and travel
west on Rte. 202 approximately 16 miles. Highmoor is on your left.
From the South: Take Exit 75 off the Maine Turnpike in Auburn
(left turn off the exit ramp). Go through Lewiston and travel east about
16 miles on Rte. 202. Highmoor is on your right.
If you are a person with a disability and will need accommodations to participate in this program, please call Highmoor Farm at (207)933-2100 to discuss your needs.
2) Estimated harvest dates
Each of the Orchard Radar sites has estimates for the start and end of the optimum period of McIntosh harvest this year. These estimates are based on bloom date and the temperatures during the first 30 days after bloom. The estimates are for long range planning only and in no way reduce the need for checking fruit maturity indicators closer to harvest. But the estimates have been pretty much on target in recent years so they have some value for planning. See Monmouth, Sanford, Gorham, Old Town)
3) Guthion could lose its registration for use on apples. The manufacturer must notify the EPA if it intends to "to extend or remove the expiration of October 31, 2005 from the Group 3 uses". Beside apples, other Group 3 crops of interest to orchardists include crabapples, lowbush & highbush blueberries, cherries, nursery stock, and pears.
If you would like to express an opinion about the need to extend Guthion registration on these crops, or conversely that Guthion is no longer a critical need for these crops, send me a message. I will collect and forward responses to the manufacturer.
Sincerely,
Glen
P
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If you are a person with a disability and will need any accommodations to participate in programs, please call the Highmoor Farm at 1-800-924-5258 to discuss your needs. Please contact us at least one day prior to the event to assure fullest possible attention to your needs.