Volume 6, No. 7
May 13, 1998
Volume 6, No. 7
May 13, 1998
Some Shower
This probably falls in the category of predictions that fell short of the mark: "showers are still in the forecast", from last week's pest message. With barely any drying, particularly in the eastern part of the state, this was essentially the longest wetting period in the last 20 years.
This past 10 days will be the test of any scab management program. It is the longest wet period observed in recent years. Depending on whether one wants to divide the rain periods up, there were any where from 5 to 7 infection periods, or simply one massive one. Scab is abundant on unsprayed trees. The results of the past wet weather won't be obvious for another one to two weeks. Breaks in scab coverage, if any occurred, most probably came around Thursday and Friday of last week, May 7 and 8. It will take at least 10 days from then for visible scab to develop.The good news is that the primary scab inoculum is virtually gone in most areas, and by early next week will be gone in later areas. It is too early to stop scab treatments, because we don't yet know how many infections have started. Check likely infection spots to see if scab is already there, and keep an eye on them for the next week or two.
Probably the best strategy for the coming week is to make sure that you maintain a protectant cover of an EBDC or captan, if you feel protection was good during the heavy rain. If you feel there may have been a break, make sure to put an SI with the protectant. A benzimidazole (Benlate or Topsin M) or Syllit with the protectant will also have some post-infection activity, but cannot "reach back" more than a couple of days.
It's also time to avoid fungicides which can interfere with mite biocontrol. Perhaps one more EBDC or one more Benlate won't have a major effect, but during the rest of the cover sprays, these fungicides become increasingly hard on predators.
There are a number of peach orchards showing quite a bit of leaf curl this season. The weather was perfect &emdash; cool and moist. The following is from the UMass Fact Sheet on leaf curl.Probably the most irritating thing about seeing the characteristic warty red leaves of peach leaf curl is realizing that it's already too late to do anything about the disease. The second most irritating thing is realizing that a single fungicide treatment would, in all likelihood, have prevented the outbreak. And to really frustrate growers, the disease often fails to appear for years, even without fungicide treatments, only to suddenly appear in epidemic proportions during a particularly wet, cool spring.
The fungus that causes peach leaf curl (Taphrina deformans) survives as spores in microscopic crevices on the tree. Spores from old infections lodge in loose bud scales and other tiny fissures, waiting for the next spring. Then, spores that are washed into buds or onto the first new leaves will cause infections if leaves stay wet and temperatures are between 50º and 70º F. Wet, cool springs keep peach growth slow, so new buds and leaves remain susceptible for a long time, and heavy leaf-curl will develop in untreated peaches. A warm spring, even if it is wet, won't produce nearly as much disease.
Once the fungus is in the leaf tissue, fungicides won't effect it. Infected leaves characteristically have reddened warts or curling. Leaves may also appear yellow, orange or purple. Infections of the new twig tissue cause swelling. In rare instances, fruit may be infected, and develop raised, wart-like growths.
As the leaf infections age, they turn gray and appear powdery. The fungus produces spores, which break through the leaf surface, causing the powdery appearance. These spores don't cause new infections, but rest in protected areas on the peach tree until the next. Infected leaves generally drop in early summer.
Leaf curl is relatively easy to prevent, even though the timing of the treatment is a little inconvenient. A fungicide spray applied in the autumn after at least 90% leaf-fall, or in the spring just prior to bud-swell, will generally stop leaf curl. If an orchard has been heavily diseased, making both fungicide applications may be necessary to deal with the large amount of inoculum. The fungicide applications should not be concentrated to more than 2X, to insure that the coverage is thorough. Fungicides need to penetrate the microscopic crevices that are protecting the fungal spores.
The most effective fungicides are chlorothalonil (Bravo) or copper compounds (Kocide, COCS, etc.). Ziram, lime sulfur or Bordeaux are useful but somewhat less effective. Check the label for rates and other use recommendations.
For the growing season when a leaf curl epidemic hits, the only treatment is to minimize stress on the infected trees. After infected leaves drop, peaches will generally produce new leaves. This new growth stresses the tree. In severe cases canker infections develop more easily and trees may fail to develop adequate winter hardiness. Severe leaf curl can ruin one season's crop, and may set the stage for more long-term problems related to stress. Minimize the stress by supplying some extra fertilizer, particularly nitrogen, irrigating, and removing the fruit load.
In peaches, shuck fall is the time to pay particular attention to signs of attack by tarnished plant bug, hickory plant bug and oak plant bug. Feeding by these insects peaks between shuck fall and when the fruit reach 1/2" to 3/4" in diameter. It is important to protect fruit at this stage against the catfacing injury caused by plant bugs.Research has shown that either Guthion or Imidan alone are at best 50% effective in preventing plant bug injury. Therefore, we suggest use of a full rate of Guthion or Imidan in conjunction with a one-third labeled rate of a pyrethroid such as Asana, Ambush or Pounce. We feel that because of the tendency of pyrethroids toward high absorption into and slow release out of the bark of the trees, the reduced rate of pyrethroid offers a good compromise; it extends the residual effects of the chemical while limiting the well-known destructive effects against mite predators.
The red mite situation looks good in most areas, as blocks receiving two oil applications show almost no ERM activity. In known problem areas, nymph counts have reached 1-2 per leaf, but no adults or second-generation egglaying have been seen as yet.Leafminer egglaying and egg development have been slowed by the weather, and no sap feeding mines have been seen. Growers who have seen captures on sticky trunk traps exceed threshold levels should consider a treatment of either Provado or Agrimek. If Agrimek is the material chosen, it will offer excellent control of ERM as well, and it is very effective against both when applied up to a week after petal fall. As always, Agrimek should be applied with an adjuvant such as horticultural spray oil to maximize effectiveness. If Provado is the material of choice, growers would be wise to trigger the application with the appearance of sap feeding mines, usually a week to 10 days after petal fall.
The relatively cool, extremely wet weather of the last week hasn't done much to spark curculio immigration and egglaying. Over the past week, we have been sampling in many commercial and unmanaged orchards; thus far we have seen no oviposition scars in apples at any of the sites. Only a handful of egglaying scars have been seen in wild plums (generally the first to fall victim to PC activity) and one PC feeding scar was found in Sterling.Trap captures have also remained low, both in the canopy and at the trunk. Traditionally, orchards are susceptible to PC egglaying during the first warm spell after petal fall; the forecasted increase in temperature for 5/14 to 5/17 will likely inspire the first significant egglaying of the year. With the lag in immigration last week, growers would be well advised to keep a sharp eye out through the weekend for the appearance of egglaying scars, and be prepared to treat.
As pears begin to set, it is time to consider options for post-bloom treatment against pear psylla. According to trials done over the past several years, Agrimek in conjunction with horticultural spray oil applied 1-2 weeks after petal fall provides 4-6 weeks of protection under normal conditions. If Mitac is to be used, back-to back sprays are recommended, with the first occurring 2 weeks after petal fall and the second 7-10 days later.To reiterate some recent information out of New York, Provado has also been assessed for effectiveness against psylla. Data over the past six years suggests that an application at petal fall (20 oz. per acre) followed by a second application within 2-4 weeks will offer control of low to moderate populations, and Pyramite (13.2 oz. per acre) has shown similar results to Provado. Both Provado and Pyramite at the high label rates have shown a reasonable ability to knock down high summer populations as well.
Pear thrips have been fairly active this year, particularly in orchards not receiving any early-season chemical treatments. In commercial orchards, up to 1-2 thrips per blossom have been seen: enough to cause noticeable damage, but not enough to have much of an economic impact. Damage caused by thrips may appear very similar to mild frost damage, with browning of the edges of the flower petals and partial closing of the blossoms. Such damage is caused when thrips feed on the tender tissues of the blossom clusters. Despite their presence in most Massachusetts orchards, it is rare to see damage exceeding economic thresholds, and thrips are generally controlled secondarily by any of the early-season insecticide treatments.
One commercial site in eastern Massachusetts is showing very high populations of green fruitworm lavae. It's a relatively new orchard carved from hardwood forest. There are early instar larvae feeding on terminal growth and to a lesser degree fruit cluster leaves, but no fruit damage to this point
Healthy Fruit is written by Dan Cooley, Ron Prokopy, Starker Wright, Wes Autio, and Karen Hauschild except where other contributors are noted. Edited by Dan Cooley. Publication is funded in part by the UMass Extension Agroecology Program, grower subscriptions, and the University of Massachusetts IPM Program. Healthy Fruit is available on the Web at The Massachusetts Tree Fruit Advisor, (click here). A text version can be e-mailed to you if you contact me, at dcooley@microbio.umass.edu. Please cite this source if reprinting information.
