West Michigan tree fruit update - Aug. 7, 2018

The dog days of summer are for insects and diseases, too.

Horticultural concerns

Peach harvest is well underway with maturity running about 5 days behind normal and a nice even pace to harvest. Apple size is normal for this time of year or slightly larger than normal. While some much needed rain fell recently, lighter soils are still too dry and irrigation should continue. The rule of thumb is to apply 1 to 1.5 inch of rainfall equivalent per week – perhaps 2 inches if you are on sandy soils.

At this time, we feel the predicted apple harvest dates are still accurate with the data collected so far. Once early apples start to ripen, we might need to tweak the dates a bit and it’s just a guide to help you plan ahead. It is time to start planning out your harvest management plan for AVG (ReTain, 1-MCP (Harvista) and Blush.

Tree fruit diseases

Summer diseases in apples include a complex of pathogens and the primary concerns are sooty blotch and fly speck. Second application of fungicides for summer diseases should be considered in the next week or so. Hot humid weather conditions are perfect for summer diseases and fruit rots to flourish.

Fire blight – with many apples now showing terminal bud set, any trauma we might get with winds or hail, should not be an issue going into August even if you do have some blight in the orchard.

Apple scab – there was a bit too much primary scab in the area and the typical drier weather in August allows you to stretch out the scab covers a bit. However, if the weather turns really wet, your fungicide program for secondary scab will need to be turned up as well. Pinpoint scab is a problem best taken care of in the orchard, especially in late August and into September if rainfall becomes heavy. Fruit rots and sunburn are also conditions to protect for.

Tree fruit insects

Adult trap numbers of codling moth continue to be very low in most blocks, but there are few problem blocks with regular trap numbers to be concerned about. I set a regional second generation biofix for July 20 (1465 DD50) and there have been 337 degree days base 50 accumulated since that date using Sparta Weather data. This indicates we are at the 20 percent egg hatch stage for blocks that have been catching moths for at least two to three weeks and cover sprays are needed.

MOST blocks have very low to no adult flight and cover sprays can be delayed by at least a week if they are needed at all. A good rule of thumb for second generation is to use your 1X trap numbers to guide you. If you get trap catches over threshold, go out 10 days from there and be ready to apply a cover spray. It’s best to use your own orchard trap numbers for decision making. Overall, codling moth pressure is not high for second generation so far, but there are hot spots with stings from first generation that need to get covered up now.

Spotted wing Drosophila trap catches continue to be high. Susceptible crops include peaches, summer raspberries and blueberries and cover sprays need to remain tight.

Adult flight of summer generation obliquebanded leafroller is happening, and it seems to be less sporadic than last week. I set a biofix for the summer flight for August 1 (2517 DD42) and 160 degree days base 42 have been accumulated since that date. Small larvae will become visible in about two weeks, just in time for Paula Red harvest where they can sometimes be easily found.

San Jose scale adults for the second generation started flying a couple of weeks ago and numbers have been high in hot spots. Crawlers for second generation should begin to appear this week in blocks with scale problems. I set a new regional biofix for July 20, 2018 (1382 DD51) with 325 degree days base 51 accumulated since that date for Sparta. The model indicates that crawlers should begin to hatch at any time with cover sprays going on in about 7 to 10 days.

Apple maggot continue to fly in the Grand Rapids area and numbers seem to be higher than in years past. The recent rain will drive even more from their overwintering sites in the soil. You cannot make effective decisions about apple maggot if you aren’t trapping for it and for the past three years or so, they seem to be on the increase. Phil and I are concerned that we have become complacent about this “old” pest, but we have trapped it in what we consider very clean blocks, so it’s around. You typically have about a week from the trap catch to get something on to prevent egg laying damage and maggot larvae in fruits.

Japanese beetles continue to be present, but seem to be declining as they should (but not soon enough, if you ask me).

All stages of European red mite and twospotted spider mites are now present. There seems to have been an uptick in mite populations over the past week or so, and more twospotted spider mites this summer than ever. The threshold for all mites is 7.5 mites per leaf for August. This is a critical time to put one last miticide on before mid-August. If you are over 7.5 mites per leaf now, it is likely photosynthesis will be compromised leading to a reduction in overall apple fruit size. If your numbers are below the threshold, it is likely that once you get past August 15, there would be no economic benefit to miticides.

From my early biofix for oriental fruit moth on May 10, 2018, 2088 degree days base 45 have been accumulated. This indicates we should be in between second and third generations and cover sprays are not as critical, but the generations start to run together as we move into late summer so use your trap numbers as a guide. Using the model, we should be at 10 percent egg hatch for third generation in about a week and cover sprays in stone fruits and perhaps apples with high populations of adult oriental fruit mth need to be covered.

Brown marmorated stink bug (BMSB) can be found on various favored hosts in all stages. I’ve decided to start calling this the Brown Maddening Stink Bug due to the fact that we often find fruit damage with no BMSB in nearby traps. Actually, this is really explained by the fact that the lures for current BMSB traps are based on aggregation pheromones and BMSB is just not ready to aggregate when there are so many food choices out there.

Also, while we are past the watchful waiting phase for this invasive on the Ridge, we are still on the low side of the population numbers compared to what other areas out east have seen and low trap numbers do tell us pressure should be lower. If you had any BMSB damage – known or suspect – in 2017, then you need to consider a whole orchard cover spray in the next week or two. Then follow up border sprays should be enough for all but those blocks that have sustained heavy damage in the past few years.


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