RI Apple IPM Newsletter
June 3, 1997
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
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.