MSU Extension

Weather and growth stages

The rollercoaster of weather continues, but on average, temperatures have been much cooler than normal and our degree-day totals have fallen back to readings more close to normal averages. Some very cold weather over the past week brought the treat of freezing temperatures, but at this time there appears to be no damage as temperatures remained above 32 degrees Fahrenheit in most fruit growing sites. Apple fruit set appears to be excellent with many kings setting well. Peaches are approaching shuck split. Sweet cherries are still in bloom in some blocks, with petal fall fast approaching.

In general, most apple varieties are still in the full bloom stage with petal fall becoming more apparent every day – it’s been a slow and drawn out bloom period this season. Growing degree-day (GDD) totals for the Michigan State University Sparta Enviro-weather station are 1,160 GDD base 32, 521 GDD base 42, 393 GDD base 45 and 231 GDD base 50. On average, degree-day totals put this area two to four days ahead of normal average accumulations.

Diseases

Several rain events over the last week have produced at least one apple scab infection period for all west Michigan areas and some had two. Primary apple scab spore numbers are declining and we should be nearing 100 percent spore maturity. It will take several rain events over the next two or three weeks to discharge all spores, so keep your fungicide program in a primary scab mode. Follow the development of apple scab infections and symptoms on MSU Enviro-weather.

With most apples in full bloom over the past week, the risk for fire blight was in the mix a week ago and much colder weather has moved in to lessen that risk. With warmer temperatures predicted for later in the week, blossom blight will still need to be considered for any viable bloom still present.

Insects

The insect world is in a bit of a standstill lately with much cooler temperatures. Later in the week, weather will improve for the six-legged creatures and their activity will increase. There seems to be no hurry to have to get your petal fall sprays on until nighttime temperatures get above 50 F, when insects such as codling moth and plum curculio are more active. Some bee hives are now being moved out, but be aware if your neighbors still have hives set before any insecticides are applied nearby.

Codling moth adult flight has not been reported. Traps and disruption should be up now. First flight usually begins at petal fall, but could be delayed in low population blocks and due to cooler night temperatures. Average biofix is 350 GDD50 for the Grand Rapids, Michigan, region and we are at 231 GDD50.

Plum curculio activity has not been reported in any tree fruit crops in the general Grand Rapids area. No controls are needed in apples until petal fall. MSU Extension advises to start looking for their damage in early-setting fruits like plums and sweet cherries – this could give an indication of their future activity. Cooler weather will slow their activity, but warmth next weekend could get them moving into small developing fruits.

A few overwintering obliquebanded leafroller larvae continue being reported feeding in terminals. Numbers are very low in general, but problem blocks need to be monitored closely for activity.

European red mite nymphs and adults can be found. No reported fresh egglaying. Petal fall is the next timing for targeting mites.

Apple rust mite should be present now as adult females. Monitoring is needed in blocks with a history of apple rust mite issues; Red Delicious is a favorite variety for rust mites.

Oriental fruit moth flight has been down due to cooler weather. A regional biofix was set for May 6 (308 GDD 45). Since that date, there has been an accumulation of 85 GDD45 using Sparta weather station data. Oriental fruit moth mating disruption needs to be up now in stone fruits to be most effective. Peak egg hatch is at least seven to 10 days away – target this timing for first management in stone fruits to prevent flagging in shoot tips. First generation oriental fruit moth is not a concern in apples, but should be monitored with pheromone traps.

Black stem borer is a sporadic pest with some heavy infestation in problem blocks. Adults have not been very active with cooler weather, but continue monitoring blocks for burrowing damage and apply trunk sprays in blocks of concern if you didn’t get it done at pink stage.

Apple grain aphids continue being reported in very low numbers. Rosy apple aphids continue being found with some curling of leaves found in unsprayed trees – none found yet in managed blocks. Monitor for green peach aphids and black sweet cherry aphids as they should begin to become active in peaches and cherries respectively. Scouts should also be taking note of beneficial insects that might be present and feeding on aphid populations.

There have been no reports of white apple leafhopper activity. They overwinter as eggs and typically egg hatch begins at petal fall and peaks at the first cover timing. The earliest nymphs are often found on the underside of older leaves.

Overwintering San Jose scale are present with no activity being reported. Males typically fly during bloom and crawlers emerge 10 to 14 days after. Traps should be in place for males in problem areas and checked regularly over the next two weeks for first flight.

Spotted tentiform leafminer adult flight is declining. No sap feeders reported yet and they should be found at any time. This is a minor pest in general.

Redbanded leafroller first generation flight is ending and egg hatch continues with small larvae found in unsprayed trees. This is a minor pest in apple and petal fall sprays easily take care of it.

Borer pests to monitor include American plum borer, which is now flying in low numbers. Lesser peachtree borers and greater peachtree borers should begin flying at any time. No dogwood borer frass and pupal cases in burr knots. Mating disruption for all borer species can start being placed now.