RI Apple IPM Newsletter

From Heather Faubert and Steven Alm

Weekly phone message can be heard by calling (401) 949-0670 from 5:00pm to 8:00am daily.

We are past primary apple scab season now. If thorough inspection finds that scab lesions do not develop in the next two weeks, then primary scab has been controlled. You can switch to a summer schedule for controlling summer diseases such as sooty blotch and flyspeck. Our general recommendation for controlling summer diseases is Captan every two weeks or Captan plus Benlate or Topsin-M every three weeks.

If you do find scab lesions now or within the next 2 weeks, follow the recommendations in last newsletter and read about eradicating scab in the 1996 – 1997 New England Apple Pest Management Guide on page 15.

We started finding plum curculio egg laying scars on May 27th. The warm, humid weather this past weekend probably brought out plum curculio in full force. We expect everyone has applied an insecticide within the last 7 days to control plum curculio. Once Guthion or Imidan has been applied a second application should be made 7 – 10 days after the first. After the second application, an insecticide should be applied only if you find significant fresh plum curculio injury. Usually only two insecticide applications are necessary but occasionally a third application is needed.

Apple blotch leafminer mines are primarily in the sap feeding stage now. This is when they are visible only from the lower leaf surface. We started finding mines that had advanced to the tissue feeding stage on May 29th. This is when the mines are visible as a collection of dots from the upper leaf surface. There may still be time to apply Lannate against the first generation mines. Provado or Agrimek should have been applied closer to petal fall. Lannate should be applied before 10% of the mines have advanced to the tissue feeding stage. Lannate is very damaging to predatory mites. Probably a better stategy at this time is to wait until early July for the second generation sap feeding mines and control them with Provado. The threshold for first generation leafminer is 13 mines per 100 fruit cluster leaves; the threshold for second generation leafminer is 2 mines per leaf.

White apple leafhoppers are easy to find in some orchards. Look on the underside of older leaves for the small, pale nymphs. White apple leafhoppers are generally controlled by Sevin in thinning sprays when used at the 1 lb/100 gallon rate. Leafhoppers can also be controlled with Thiodan and Provado (at 1 oz./100 gallons). Provado is a systemic insecticide and lasts a long time in the foliage killing pests. Another leafhopper, the rose leafhopper, looks nearly identical to the white apple leafhopper. The rose leafhoppers overwinter on rose plants and the first generation adults can migrate into apple orchards in early to mid June. These adults lay eggs on apple which hatch into nymphs. These nymphs cause the same injury to apples that white apple leafhoppers so (white stippling on leaves and dark spots of excrement on fruit and leaves). The rose leafhopper can complete 2 more generations on apple before returning to rose in the fall to spend the winter.

European red mites have started laying eggs, beginning their summer generations. The choices for summer miticides are slim. In addition to Kelthane and Carzol there is a new miticide from BASF called Pyramite. As soon as it is available in Rhode Island and we know more about it, we will pass on the information to you. An alternative approach to miticides is to use a preventative summer oil program. Cornell has conducted field trials for the past few years to evaluate the effectiveness of using highly refines oil in a seasonal to control mites throughout the summer. Some examples of these products are Sunspray Ultra Fine Spray Oil (Sun Refining & Marketing, Philadelphia), and Stylet-Oil (JMS Flower Farms, Vero Beach, FL).

Their approach is to make three applications, on a preventive schedule: immediately after the bloom period, before mite populations have a chance to build. The first application can be any time from petal fall to 1-2 weeks later, followed by two additional sprays at 10-14 day intervals. The oil is not concentrated in the tank, but rather mixed on the basis of a rate per 100 gallons of finished spray solution. For instance, at the one gallon rate, a spray tank holding 500 gallons receives 5 gallons of oil. The sprays are applied at a volume sufficient to obtain adequate coverage of the canopies – they recommend 100 gallons per acre.

Dosages tested by Cornell are 6.5 oz., 1 qt., and 1, 2, and 3 gallons/100 gallons of finished spray solution. Results of their tests can be summarized as follows: the 2 and 3 gallon rates effectively controlled mite populations for the entire season in all but the most extreme cases. The 1 gallon rate maintained control of moderate populations but was not as effective against severe mite pressure ( a fourth spray was necessary later in July). The lower rates provided only minimal control, permitting unacceptable mite numbers by mid-July in orchards with moderate or severe populations.

One undesirable consequence of the oil treatments can be the occurence of small necrotic lesions on some of the leaves in blocks receiving the highest rate, particularly 2 and 3 gallons. Foliar injury tends to occur mainly in those portions of the canopy where spray has dried unevenly or else accumulated after application, especially in locations adjacent to the sprayer and at the ends of terminal leaves. However, the oil caused no leaf drop, even in cases where the trees were under moisture stress. Fruit samples taken at harvest to check for any effects on fruit quality showed no differences in fruit color, raised lenticels, or finish problems in the treated fruit compared to untreated fruit. The only adverse result was an increase with oil rate of a varietal stippling characteristic in the skin of Red Romes, known as “scarf”. Certain other varieties, such as Staymen, Jonathan, and some Red Delicious strains, also exhibited this characteristic to some degree, but the oil tended to make it worse in Cornell’s trials.

Overall, the results of this work demonstrate that summer oil applications can be used to effectively control red mite populations in many orchard situations. So far, mites have not demonstrated an ability to develop resistance to oil, and oil is less toxic to at least some beneficial species than are traditional toxicants. Although it is possible to kill some predator mites by directly spraying them, overall mortality is not very high.

Some drawbacks to this management strategy are:
– relative high cost of a complete summer program
– phytotoxicity or fruit finish defects in some situations or on certain varieties, especially when applications take place at high temperatures or under conditions of moisture stress
– essential need for complete spray coverage to maximize effectiveness
– and, most importantly, compatibility problems with some fungicides needed to control summer diseases, particularly Captan.

Some principles to guide the use of summer oils:
– oil appears to be capable of killing both eggs and motile mites, but is probably acting more against motile forms in summer airblast applications (the coverage is usually insufficient to suffocate the eggs)
– multiple sprays are necessary to control even moderate populations
– summer oil sprays must be started when mite populations are low.

Once the second insecticide application is made against plum curculio, growers can usually not spray another insecticide until it is time to control apple maggot fly – usually sometime in July. Be sure to take advantage of this lull of insect pests and don’t spray insecticides unless you have an unusual problem. In nearly all cases, green apple aphids do not require an insecticide application, rather beneficial insects such as syrphid fly larvae, the orange cecidomyiid fly larvae, and ladybugs almost always control aphids – you just need to be a little patient.

Our RI Fruit Growers Summer Tour is happening on June 27th. We’ll be meeting at the Greenville Cooperative Extension office at 12:00. >From there we’ll travel to the Tougas Family Farm in Northborough, MA. It is sure to be a great tour so get your reservation in early to Al Hersey.

The International Dwarf Fruit Tree Association is holding a summer tour in Massachusetts this year. On Monday, June 23, the group will tour Gibbet Hill Orchards in Groton, Honeypot Hill Orchard in Stow, Tougas Family Farm in Northborough, and Sunny Crest Orchards in Sterling. On Tuesday the group will tour Western Mass. For more information contact Wesley Autio at UMASS, phone number (413) 545-2963.