AppleTalk Conference Call Summary
Tuesday, May 31, 2016, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments,
May 31st Call download: Click Here
Crop update
Growers who experienced freeze damage on May 15 are continuing to assess the extent of damage by checking growing fruitlets for seed quality and size and making notes of external damage, e.g., frost rings, blemishes. Although these observations will help direct management tactics going forward, many will be waiting to make a more accurate evaluation of the crop following ‘June drop’. Many growers with injury have decided to not apply chemical thinners this season.
Observations on the utility of Promalin with Tom Ferguson, Ferguson’s Orchards
Ferguson’s Orchards applied Promalin (gibberellins A4A7, 6-BA) to select blocks at their Chippewa Falls, Eau Claire and Galesville Orchards within 12-19 hours after the May 15 freeze. At time of application, and for days following, temperatures were below the recommended 65°F and crop phenology varied from petal fall in Chippewa Falls to 6-10 mm in Galesville. Tom believes that the Promalin application had little to no impact on setting the injured fruit. Rather the greatest factor in fruit viability was elevation and length of time the fruit were exposed to the critically low temperatures. He noted that the apples that are ‘sticking’ have green tissue and seeds.
Insect management
Codling moth
Many growers from western Wisconsin to the southeastern part of the state have set a biofix for first generation codling moth (CM) on May 23 or 24. Biofix is marked by a significant biological event, or first sustained flight, where moths are captured multiple days in a row or exceed a threshold of five moths per trap per week. Once a biofix date is established start tracking degree days, base 50°F, to time the first larvicide application at 250 or 350 DD.
The total population for each generation emerges in the shape of a bell curve over a 600 to 900 degree-day period, where we typically have 1000 degree days between each generation of a biofix. This suggests that after 250 DD from biofix, only a small portion of the total population has emerged, i.e., 3% hatch. Orchards with high pressure or a large first flight, e.g., more than 10 moths per week, often apply the first larvacide at this time. If the initial flight is light or inconsistent due to cooler temperatures or rain a stronger flight can occur after the first biofix, e.g., two-weeks later. If this is occurs the first larvicide can be applied at 350 DD. Growers with a lot of frost damage can also choose to delay their first larvicide until 350 or 400 DD if trap captures are low, e.g., 5-10 moths per week. At 350 DD from biofix, 15% of larvae have hatched and at 450-550 DD up to 50% larvae hatch. If five moths are captured over the extent of the orchard, there is no need to apply a larvicide. If one or two traps exceed threshold, it is recommended to apply a larvicide to the entire area.
Current trap capture data is showing that areas of the orchard that escaped frost have higher captures v. lower areas with frost damage. Regardless of trap captures, it is important to note that the small fruitlets are attractive and female CM will effectively find them regardless of the fruit density.
Note: Codling moth fly between 6-11 PM and will not fly when wind is in excess of 3 MPH, temperatures are below 60°F or if it is raining. Assign the biofix date for the warmest, calmest night. When checking traps, fluttering CM had likely flown within the last 48 hours. Most female CM can live for seven to 10 days, yet will mate and deposit the majority of eggs on the evening they emerge.
Plum curculio
Plum curculio (PC) oviposition (egg-laying) injury is being found in the interior of a number of orchards that have only completed a perimeter application, i.e., insecticide applied to the first 3-4 rows from perimeter. This damage on the interior of the block could have been caused by PC that had moved into the orchard during bloom or the early petal fall period before an insecticide was applied or by the weevil consuming a sublethal dose of insecticide before moving past the perimeter trees. It is important to note that Avaunt (indoxacarb) and Actara (thiamethoxam) do not have the same knock-down potential of organophosphates, e.g., Imidan (phosmet), and it may take the PC feeding on multiple fruitlets, e.g., 10-15, before ingesting a lethal dose.
We can use a degree-day model from 95% McIntosh petal fall to predict the end of PC migration from overwintering sites. After the accumulation of 308 degree days, base 50°F, PC will no longer be moving into orchards from overwintering sites. If no additional injury is found at this time, insecticide applications targeting PC may cease. If you have suffered a significant amount of damage from freeze PC pressure may continue longer, continue to use vigilance while scouting to determine if damage is continuing.
Woolly apple aphids
Woolly apple aphid (WAA) colonies are beginning to appear in earnest in historic hotspots. Scout for developing colonies on pruning cuts and vegetative shoots. Although there are many effective beneficial insects which can help control WAA, applying an insecticide early, e.g., before third cover, if WAA is a chronic pest will help manage damage. If Movento (spirotetramat) is used it can tank-mixed with a penetrant, LI 700, to increase efficacy. Note: Do not apply captan within two weeks of using a penetrant.
San Jose scale
Monitoring for San Jose scale (SJS) crawlers should begin across the region. Monitor known hotspots with black electrical tape applied to infested scaffold branches. With adhesive side towards tree, wipe a thin layer of petroleum jelly on the outside of the tape. If populations are high, concentrate a few traps in areas with greatest pressure. Increasing the number of monitoring sites may help eliminate false negatives. Low trap captures do not reflect overall pressure, i.e., false negatives. Low trap captures may indicate the beginning of the hatch. First generation SJS hatches over a narrow period, while second generation hatches over a wide period. Catches of 10-15 crawlers in a couple of days or 10 crawlers on one tape with zero on all other tapes, may warrant application.
Disease management
Apple scab
At several orchards across the state scab lesions are beginning to appear on leaves about halfway up this year’s growing terminals. This suggests infections occurred during the infection period in early May. This year, between bud break and the end of primary scab season, the number of infection periods varied between four and eight. Inspecting the number of leaves from the base of shoot and comparing to infection periods is helpful method to determining the timing of an infection.
If scab lesions are 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; Captan 50 is 64 lb./acre/year. 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 late June and July are dry, scab will go into a dormant stage. These lesions may appear to be burnt out, but will become active again when cooler temperatures return in the fall. Only apply captan on varieties where scab is present since the conidia spores do not travel far.
Powdery mildew
Powdery mildew (PM) infections are becoming visible on growing terminals. Symptoms on the leaves appear as white, felt-like patches of fungal growth with a pinkish-red discoloration or hue on the leaf margin. 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. Growers can remove and destroy infected shoots to remove the inoculum from the orchard.
Historically, 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. Fungicides labeled for PM should be applied to these varieties until shoot growth stops.
If needed, Rally (myclobutanil) can be tank-mixed with captan to offer add protection. Rally is also very effective at disrupting rust infections that occurred during bloom. Another option for PM control would be to use sulfur, an excellent protectant. If PM needs to be controlled in larger trees, and scab is present, chose an older fungicide that you may already have scab resistance to, e.g., Rally, instead of using a newer fungicide, e.g., Aprovia (benzovindiflupyr), Fontelis (penthiopyrad), that are still extremely effective for scab. Note: Do not apply captan or sulfur with oil.
