June 9, AppleTalk Call Summary

June 9, AppleTalk Call Summary
AppleTalk Conference Call Summary
Tuesday, June 2, 2015, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments,

June 9th Call download: Click Here

Apple scab
Many orchards are clean and free of scab. Scab that has been observed at several orchards across the state all have lesions appearing on leaves about halfway up this year’s growing terminals. This suggests infections occurred during the infections in early May. The number of infection periods varied between three and five, between bud break and the end of primary scab season. Inspecting the number of leaves from the base of shoot is a better indicator of timing of an infection.

If primary scab is found in the orchard it is not advised to apply any systemic fungicide to “burn out” the visible infections. Variable rates of Captan should be applied prior to wetting events. The maximum amount of Captan 80 that may be applied during the season is 40 lb. per acre and 64 lb. for Captan 50. If secondary infections are present deciding how much captan to apply should be determined by the amount of forecasted precipitation.
Protection for secondary scab infections may be applied prior to wetting events. If we find that it dries out in late June and into July, scab will go into a dormant stage. This may appear to be burnt out, but will become active again when cooler temperatures return in the fall. Conidia spore do not travel far, do not need to apply captan to all cultivars, only varieties with scab present.

Powdery mildew and rust
Powdery mildew and cedar apple rust have been very minimal across the region. Where powdery mildew has been found, these have been in locations which made minimal applications of sterol inhibitor fungicides. The key times to treat powdery mildew are between pink and petal fall. Once growing terminals have shown powdery mildew, no curative action can be taken. These terminals will die and not produce buds for the next season.

Our region does not have issues with PM causing russeting on fruit. Major problems and economic loss can effect young bearing or non-bearing trees that are still reaching vegetative maturity. Materials for PM should be applied to these varieties until shoot growth stops.
Cedar apple rust infections on fruit occurs from tight cluster through petal fall. Captan and mancozeb, e.g., Penncozeb, Manzate, applied through second cover will provide adequate protection.

Rally (myclobutanil) can be added to captan and mancozeb at petal fall to combat powdery mildew and is very effective at disrupting rust infections that occurred during bloom. Another option for powdery mildew control would be to tank-mix sulfur with captan and mancozeb at the tight cluster and pink, then apply captan, mancozeb and Rally at petal fall. Note: do not apply captan or sulfur with oil.

Codling moth
Codling moth biofix dates have been set between May 14 and May 30. Many of these biofix dates were set based on consistent, but low trap captures that had not gone over threshold. The hot weather from June 6 to 8 may bring a stronger flight. If high captures are caught this week, consider resetting the biofix for this flight. Larry Gut discusses the concept of setting biofix based on a “significant biological event”, e.g., five codling moths found in a trap overnight versus over a two-week period. This would include high trap counts going over threshold, when flights have otherwise been low this spring.

Key parameters for codling moth flight:

  • Temperatures above 62F
  • Wind below 2-3 mph
  • No rain

Lesser appleworm
Orchards participating in Threshold or IPM Institute scouting programs should all have atleast one LAW or OFM trap in their orchards. We have yet to catch any OFM, but are consistently catching LAW. There is not established threshold for LAW, a nominal threshold of 10 has been set by John to indicate when populations are high enough to warrant treatment. Fortunately, LAW has very similar timing with its life cycle and high LAW trap counts could justify treating CM/LAW at 250 DD from CM biofix, even if CM numbers have been low.

Remember to rotate modes of action: Each generation of codling moth should be treated with an insecticide with a different mode of action. This becomes more complicated when management of other pests, e.g., PC, AM, aphids or leafhoppers, overlap with codling moth management.

Heavy rains will wash of any material applied for CM. See this updated article from John Wise, Michigan State University, on rain-fast characteristics of insecticides, http://msue.anr.msu.edu/news/rainfast_characteristics_of_insecticides_on_fruit.

Location Biofix date DD accumulated by 6/8/15

  • La Crescent, MN May 30 125 DD
  • Galesville/ Trempealeau, WI: May 14; May 25 297 DD; 211 DD
  • Lake City, MN May 26 193 DD
  • Chippewa Falls, WI May 28 147 DD
  • Beloit May, 15
  • Lake Winnebago May, 24 186 DD
  • SE May 23 (one of many)

Plum curculio
Orchards which had a mid-May McIntosh petal fall, have accumulated 225 to 275 degree days from May 15. We need 308 degree days, before emigration of PC from overwintering sites end. While scouting for PC it is important to differentiate new from old injury and if injury is found along the perimeter or further into the orchard. Old injury will have a crescent shaped scar enlarging or depressing in fruit. Additionally, exudate can seep out of fruit. This is especially important if only perimeter sprays have been applied. We have not seen any signs of apple curculio at this time.

Mullein plant bug
Significant levels of mullein plant bug have been found along the edges of many orchards. The nymphs are pale green and the adults are oval shaped and about 1/10th of an inch long. Eggs overwinter on woody hosts, including apple and pear. There are three to four generations and summer generations will eventually move to other broadleaf weed hosts, i.e., mullein.

This is both a pest and predator with adults feeding on aphids and thrips. The overwintering generation hatches from tight cluster to petal fall and this early generation has likely caused much of the warty damage to fruits that we see around the perimeter of orchards.

Injury, see Figure 2 can be seen as a small bump, the size of a ball point pen. If adult mullein plant bug are seen it trees, it is likely orchard floor is clean, e.g., does not have a lot of blooming vegetation.


mullein plant bug

Figure 2. Mullein plant bug injury to apples

European red mites
We are now beginning to find European red mites throughout whole blocks. Recent sequential samplings are finding that mites are below threshold and with frequent rain and actively growing terminals, trees should be able to with stand current levels of feeding that may be present. The June threshold for mites is an average of 2.5 mites per leaf. This includes mites at all life stages, but not eggs.

ID hotspots to be prepared to do threshold sampling when weather becomes warm and dry.

Rosy apple and green apple aphids
Aphid populations have been very low this spring. Rosy apple aphids will often establish colonies on the actively growing water sprouts and can be found throughout the tree canopy. Typically we have some really good biological controls of RAA including gall midge maggots and lady beetle larva and syrphid fly maggots. RAA will eventually move to other broad-leaf weed hosts.

The Lake Ontario IPM program recommends the following: Chemical control is recommended if more than 5% of fruit clusters are infested and few predators are identified. Monitor for aphid predators around rosy apple aphid colonies. Beneficial insects may make chemical control unnecessary.

Green apple, apple grain aphid or spirea aphid, all different species, but indistinguishable to the untrained eye are beginning to appear. Unlike RAA, these will continue to infest terminals throughout the canopy and can be a season long secondary pest. They rarely require their own treatment and neonicotinoids applied for plum curculio of apple maggot should suppress these populations. Management is more critical on young, non-bearing trees as it will reduce vigor and growth of shoots. Honeydew produced by the aphids may drip onto fruit allowing sooty fungi to grow.

The Lake Ontario IPM program recommends to begin monitoring at petal fall and continue until terminals harden off (late July or August). Check 100 terminals in a 10- 15 acre block weekly throughout the summer. Pick 10 terminals per tree on 10 trees randomly, without visual bias towards infested terminals. The action threshold for green apple aphid is 400-600 aphids per terminal on 10% or more of terminals checked. Be sure to scout for presence of predators when assessing aphid populations in orchards. If more than 20% of the aphid colonies have natural enemies, delay or eliminate an insecticide application. Resample orchards with high numbers of natural enemies present within a week to see if predators are providing control.

Weed management
Growers who have not applied an herbicide and still want to, may consider mowing weeds and treating when they are actively growing. Some herbicides will lose their efficacy once weeds are beginning to develop seeds/blooms. Tall weeds may also not get the best coverage from the herbicide boom. If the boom is pushing over tall grass, while the application is going on, this is not good.

Where problem weeds are present, or did not respond well to the last herbicide treatment, use an herbicide with a different mode or action or consider applying an herbicide with multiple modes of action.

If you have a site where you are considering replanting trees in 2016, start managing your weeds now with cultivation, cover crops or herbicides. A season or two of managed herbicides prior to planting a new orchard will pay off.