Fruit Size
Dry weather continued last week in most areas of Southern New England. Spotty thunderstorms provided needed relief in some locations. In spite of the dry weather, fruit appeared to grow well. Fruit diameter in monitored blocks of McIntosh, Delicious, and Gala were 2.06 in., 2.18 in., and 2.22 in., respectively. Bloom occurred at the normal time this year. Unless dry weather and high temperatures stress trees excessively in the next few weeks, a normal time of harvest is anticipated. Hand thinning in heavily set blocks destined to receive ReTain is suggested.
Leaf Sampling
Leaf analysis is the only accurate means of assessing nutrient needs of fruit trees, since it measures the actual quantity of nutrient elements that is able to make it into the tree. It is time to begin collecting samples.
General Procedures
- Collect leaf samples between July 25 and August 15.
- Sample when leaves are dry.
- Sample leaves from the mid section of this year's growth. Leave the petiole (leaf stem) attached to the leaf.
- If you have used nutrient or fungicide sprays containing nitrogen, boron, magnesium, zinc, copper, or manganese, wash the leaves in clean water with a mild detergent (dishwashing liquid). Rinse them three times in distilled water. Do not soak the leaves in water. After washing, dry on paper towels.
- Place leaves from a single sample in a paper bag and label it as to the block, variety, rootstock, age of tree, crop load, and general condition.
- Send samples to the Soil and Tissue Testing Laboratory, West Experiment Station, University of Massachusetts, Amherst, MA 01003 along with a check for $15 per sample made out to the University of Massachusetts.
For Assessment of General Nutrient Status
- Select 10 trees of the same variety and similar age, rootstock, crop load, and general condition within the block to be assessed.
- Collect ten leaves from each tree. Select only healthy leaves.
- Combine these 100 leaves into a single sample and treat as described above.
To Diagnose Problems
- Collect at least 50 leaves from trees of the same variety and similar age, rootstock, crop load, and general condition that show the symptoms. Combine these leaves as a single sample and treat as described above.
- Collect at least 50 leaves from similar trees in the block that do not show the symptoms. Combine these leaves as a single sample and treat as described above.
Disease Problems?
Yes, there is still a plant pathologist on the apple team. In general, the recommendations for treatment of tree fruit diseases recently have been so dull that I'm sure most of you haven't been bothered by a not seeing them in Healthy Fruit.
Right now there are a few points worth making regarding apple scab and the summer blemish disease, sooty blotch and flyspeck. Regarding scab, there has been a little secondary spread, but no major scab weather. As growth stops, tender new leaves which are most susceptible to scab will no longer be available. As trees mature, they become more resistant to scab. The heat has also helped this year.
Summer blemishes are a bit trickier. It has been a dry year. However, it has also been a humid year. For the flyspeck fungus, we suspect that very high humidity is just about as good as wet weather. Muggy nights, where the dew point is 72º and the temperature is 72.5º are ideal for growth of the fungus. At this time of year, we think spores are released as conidia from the wild plants bordering orchards, particularly during the early morning as the plants dry. These spores land on the apple fruit, among other things, and over a period of 2 to 4 weeks (perhaps even longer) grow to form "specks".
The humidity situation can be improved more by summer pruning. Summer pruning does two things. It improves the "weather" in the tree canopy. Canopies retain humidity and moisture, and the thicker a canopy, the longer it will stay wet and humid following rain or heavy dew. Summer pruning also improves the spray coverage and penetration in trees. Both of these factors will help eliminate flyspeck and sooty blotch in a block.
The farther apple trees are from the orchard border, the less likely the fruit are to get flyspeck. While we haven't tested the efficacy of doing it, we suspect that knocking back the orchard border by 30 feet or more can reduce flyspeck.
Obviously, timing summer fungicides in a year with erratic rains can be difficult. Dave Rosenberger's estimates of fungicide longevity help make the call. At this time of year, Benlate or Topsin M combined with Captan 80 (3 oz. + 5/8 lb. per 100 gal.) will last at least 3 weeks between applications, unless there is more than 3.5 inches of rain on Benlate or 2.5 inches on Topsin M. Captan alone (5/8 lb. / 100 gal.) will last for at least 2 weeks, or 2 inches of rain. If the residue it leaves does not bother you, then ziram plus sulfur (1 lb. plus 1 lb. per 100 gal.) will last well, for 21 days or 3.5 inches of rain. Do not forget that adding calcium sprays will help with summer blemishes.
What about the new fungicide, Sovran? The honest answer is that no one knows what it will do. It appears that it will be quite effective against summer blemish diseases, but there is not any information on timing. And right now, it is expensive, and this new chemistry can cause resistance to develop. Right now, it makes more sense to save Sovran for scab, and use the older fungicides in the summer.
Flies Wide Shut
For the past several weeks, we have predicted that this year's threat of apple maggot damage will be both early and light. In fact, the AMF population has remained low, as captures on unbaited monitoring spheres currently average 1 AMF per trap. Roughly 50% of orchards statewide have exceeded the recommended threshold of 2 AMF per unbaited monitoring trap, placing the timing of this season's AMF immigration on par with that of the last 2 years.
At this time of the year, AMF pose the most direct threat to early-ripening cultivars (most commonly Jersey Mac), and have been known to cause substantial damage in July to varieties which offer the most appealing early egglaying sites. Because of this, growers should pay particular attention to capture levels on traps in early cultivars, and spray accordingly. As always, a reduced-rate treatment with Guthion or Imidan should offer complete early-season AMF control, and sprays offer the greatest benefit when triggered by trap capture thresholds.
The Usual Suspects
Most orchards receiving either a full oil program or an early-season miticide remain free of significant mite buildup, despite the blazing temperatures of recent weeks. A few growers have spot-treated areas of perennial concern, and bronzing has been observed on the usual suspects, such as Red and Golden Delicious.
There are no simple solutions on summer mite management, as use of available materials may impact buildup of predators, lead toward pest resistance, or be incompatible with summer disease management tools. Growers who do see a need for summer treatment have the options of Kelthane, Carzol, Vendex, and Vydate, each with known drawbacks; Apollo, bearing in mind the 45-day PHI; and Pyramite, currently seen as the best available alternative.
Leaf Miner's Daughter
The bulk of second-generation leafminers have progressed into the tissue-feeding stage, though (as is typical of summer leafminers) wide variation in growth has been observed, even within orchards. Most orchards remain remarkably clean, considering the pressure from first-generation adults. It seems that chemical controls (particularly Provado) used against the first generation hold the potential for season-long control in most blocks, though some orchards may experience a third-generation population explosion, as was seen last year. Studies in New York suggest that there is little advantage to be gained by treating the third generation of LM, as the majority of damage appears to be caused by feeding of the second-generation miner larvae.
