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Jon Clements has been on the job for about three weeks. A number of you have met him at twilight meetings or at your orchards. If you wish to have him visit or have questions for him, he can be contacted via the following methods.
Address:
Jon Clements
UMass Horticultural Research Center
391 Sabin Street
Belchertown, MA 01007Telephone: 413-323-4208
Cell phone: 413-478-7219
Fax: 413-323-4875E-mail: clements@umext.umass.edu
Over the last ten years, we have discussed, on a number of occasions, ways of reducing apple tree growth and of encouraging flower bud formation. These techniques are particularly useful in settings where trees are planted too close or where trees are relatively young but appear uninterested in fruiting.
Girdling is one of the most reliable approaches. It can take the form of a single cut made with a knife completely encircling the trunk at the base of the tree (referred to as scoring) or a similar cut but with the removal of some bark tissue (referred to as ringing). Scoring is easily performed with a curved linoleum knife, and ringing can be done with a saw (for 1/16 inch cuts) or with a specially designed ringing tool (for 1/8 inch to 1/4 inch cuts). This is best done when terminal growth is between 4 and 6 inches, but it will be effective somewhat later. Generally, we recommend not girdling weak trees. It is best to use scoring primarily and ringing (with a saw) only sparingly.
For situations where the crop is lost due to frost or hail, ethephon can be an excellent treatment for reducing vegetative growth. Apply ethephon at 1.6 pints per 100 gallons dilute (500 ppm) when growth is 4-6 inches and again a month later if needed at 1 pint per 100 gallons (300 ppm). Do not use ethephon on fruiting trees, since it will cause some thinning and early fruit drop.
Growers should be carefully monitoring their orchards (both peach and apple) for signs of trunk borers. The greater peach tree borer infests it’s namesake, while the dogwood borer attacks apples. Infestations by either borer can build over time, resulting in girdling and death of trees. Conditions that favor infestation should be avoided. These include: use of spiral plastic mouse guards; dense growth of weeds and grasses around the trunk; and planting of dwarfing rootstocks with the shank over-exposed (graft union too high). Dwarf apple trees with burr-knot formation on the rootstock or graft-union area are particularly attractive to dogwood borer. Signs of borer infestation include: trees that leaf-out but fail to grow (a symptom of girdling); frass and sap exuding from the trunk at the base of the tree; and borer exit and entry holes. Sometimes the signs of activity are hidden under mouse guards or weeds. Be sure to get down on your hands and knees, remove mouse guards and/or weeds to expose the trunk at ground level -- this is where trunk borers prefer to do their damage. To prevent borers from attacking your orchard, be sure to maintain a clean, weed-free environment around the base of your trees, and avoid the use of any solid plastic mouse guard. Annual trunk sprays of Lorsban 4E are a good precaution against borer attack, particularly in peaches. (Consult the Peach, Pear, and Plum Production and Pest Management Guide for details on use and timing.) Also, mating disruption using pheromones appears to be a promising alternative to Lorsban trunk sprays -- for more information see an article in the Michigan State University’s Fruit Crop Advisory Team Alert dated April 11, 2000 ( http://www.msue.msu.edu/ipm/fruitCAT.htm).
Any time now you can start to remove vigorous young apple shoots that originate in the half-foot or so below terminal shoot growth (the leader), a technique known as stripping in young trees. Removing these upright shoots will prevent competition and stunting of the central leader, which you generally want to protect -- whether growing central-leader, slender-spindle, or vertical-axis trees. Usually two to four shoots originating just below the terminal shoot are removed by stripping them off with your fingers (be careful not to strip too much!), or using sharp hand pruners. The technique is used in first, second, and sometimes third leaf trees to keep the leader rapidly growing skyward. Young shoots originating farther down the leader also need to be clothes-pinned in the first and second leaf to form desirable crotch angles. Stripping and the use of clothespins are the two most important things you can do to properly train young apple trees.
Dark, rainy, and cooler weather has besieged us. These weather conditions make it more likely your petal-fall thinning treatments (assuming you already applied them) will take hold. In fact, we are observing some good differentiation of fruitlet sizes in clusters, and it¹s not too hard to tell which fruitlets are likely to stick and which ones are history. Some fruitlet clusters are down to zero, one, or two fruitlets -- which is good -- while others still have three to four, which is not so good. Some of these may discontinue growing and eventually fall off during June drop. But to be sure they do, you still have an opportunity to go on with a little more thinner, and -- particularly with this cloudy weather -- expect good results. Caution is advised, however, and we suggest using low to moderate rates of NAA (4-5 PPM), or Sevin XLR or Accel alone. (Remember that Accel needs warm temperatures during application to perform well.) If you are looking at a variety or block where fruit set appears to be a little heavier, consider a tank mix of NAA with Sevin XLR, or Sevin XLR plus Accel. (But do not mix NAA and Accel as pygmy fruit may result!) Remember that thinners become much less effective as fruit size exceeds 10 mm, so this week is probably your last good shot at chemical thinning.
Apples in eastern areas have 3/8 inch fruit while apples in western areas have 1/4 inch fruit. The shucks are falling from the peaches.
The rain, drizzle, high humidity, and wind of the last several days have made an already tricky scab season far worse. Even though ascospore maturity (over 90%) and day degree accumulation put us well into the final phase of scab season, it is not entirely over yet! Very little scab has shown up on leaves so far from April infections, but it would be surprising if current conditions didn't result in some significant infections if trees are not protected. Most growers are planning to spray as soon as they get a window of opportunity.
Extended periods of rain also favor development of flyspeck and sooty blotch in the woods and hedgerows around the orchards, so we looked at flyspeck ascospore maturity on blackberry canes at Belchertown and Shelburne and to our relief found no development yet.
For the past several weeks, we have monitored plum curculio abundance and activity across blocks in 12 commercial orchards. In 288 traps placed in association with trees in perimeter rows, captures have declined steadily since the heavy influx sparked by hot weather in early May. Total PC trap captures thus far have yielded the following: 5/8-5/10 (43); 5/11-5/13 (24); 5/15-5/17 (16); 5/18-5/20 (7). This decline in trap captures was expected, and is likely the result of both effective petal fall treatments (reducing the number of PCs active in orchards) and the remarkably cool weather conditions of the past 10 days (aborting further immigration of any PCs remaining outside orchards).
Logically, PC damage to fruit has also remained very low, as the most recent full sample round (5/18-5/20) showed only 10 stings on nearly 6000 sampled fruit. All data from private consultants, pooled with our own observations, indicate that early-arriving PCs were successfully controlled by the first round of sprays, and those few that may remain in the orchard have been largely inactive.
This raises the question of a resurgence of PC immigration with the trend toward warmer weather forecasted for late this week (5/26). On traps intended to capture PCs immigrating from overwintering sites into orchards, we have seen no more than a trickle in the past week, suggesting that very few PCs have moved toward, into, or through orchard blocks as the residual effectiveness of petal fall treatments dwindles. Thus, it is likely that a border-row treatment will be sufficient for PC control as soon as the conditions allow—providing effective control of what we believe is the tail end of PC immigration.
To clarify last week’s recommendations toward proper timing of treatments against first-generation mines, the following is drawn from the 2000 March Message:
One question that arose repeatedly in 1999 involved optimum timing of post-bloom sprays against first-generation mines. The major concern was if Provado applied at petal fall would have enough residual activity to control larvae that hatched and entered leaves one or two weeks after petal fall. The answer appears to have been a resounding “yes!” Provado sprayed at petal fall did a great job of control in Massachusetts and Connecticut. Additional information on the residual activity of imidacloprid (the active ingredient of Provado) in leaves came from a 1999 study in Israel, where imidacloprid remained highly lethal to whiteflies arriving on tomato plants up to 15 days after application but toxicity declined quite rapidly after that. On the flip side, some orchards in [the Northeast] experienced somewhat less effective leafminer control using Provado applied 10 days or more after petal fall, probably because some larvae were already too advanced in development by then.
Development of first-generation mines has remained slow under the cool, wet conditions of the past week. With this, the window of opportunity for first-generation LM control with Provado, SpinTor, or Agri-Mek is still open, but likely not for long.
Despite the weather, a few European red mites have reached the adult stage, and light egglaying has been observed. Given this development, it is unlikely that treatment with either Apollo or Savey at this point will yield optimal results, as 1999 data from New York indicate that treatment timed at petal fall (with either material) offers the most durable control.
Growers who have not applied an early-season acaricide are advised to keep a sharp eye on the developing mite populations, and consider the treatment options carefully as the season progresses. We will discuss sampling tactics and treatment options in upcoming issues of Healthy Fruit.
Healthy Fruit is written by Dan Cooley, Ron Prokopy, Jon Clements, Starker Wright, Arthur Tuttle, Wes Autio, and Duane Greene except where other contributors are noted. Publication is funded in part by the UMass Extension Agroecology Program, grower subscriptions, and the University of Massachusetts IPM Program. A text version can be e-mailed to you if you contact Doreen York. Please cite this source if reprinting information.
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