July 10, AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, July 10, 2018, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

July 10th Call Stream: CLICK HERE

Question from growers: What effect would field crops like corn, soybeans or hay have on apples when planted near the orchard? Is one better than the other?
Different crops can have drastically different effects on orchard pests. Forages like alfalfa will increase likelihood of potato leafhopper migrations and tarnished plant bug, while soybeans may attract stink bugs and two-spotted spider mites. Corn has a relatively low potential for pest migration into adjacent apple crops. Planting floral resources for beneficials and pollinators would be the most ideal. The more edge an orchard has, the more external pressure from pests it will experience.

Woolly apple aphid
Aerial colonies of woolly apple aphids (WAAs) are beginning to develop, which is rather late compared to previous years. Each grower should respond differently to an increasing WAA population based on historic pressure and scouting for biocontrols, such as, parasitic wasp (Aphelinus mali), syrphid fly larvae and generalist predators that can affect WAA colony growth.

The insecticides Movento (spirotetramat) and/or Beleaf 50 SG (flonicamid), remain the best insecticide options to manage WAA, yet need to be applied at petal fall or first cover to offer best performance. If these applications were not made, assessing WAA pressure now is critical. If areal colonies are observed and still remain small and isolated and you still have growing terminals on trees, an application of Beleaf 50 SG may offer some efficacy or slow down population growth enough to allow beneficial insects to keep populations low later in the summer. Both Beleaf 50 SG and Movento are sequestered into the tree through young and succulent growth. Once terminal buds are set and shoots stop growing, it is less likely for these two insecticides to offer their desired level of management.

Closer (sulfoxaflor) may perform better than neonicotinoids since it belongs to a newer subclass of insecticides that have not been widely used. Do not apply a sticker-type adjuvant, e.g., NuFilm, with insecticides for WAA since the insecticide needs to penetrate the white-waxy coating of the colonies to be effective. Azadirachtin, e.g. Neem oil are probably the best option for organic producers.

For more information on WAA, visit http://blogs.cornell.edu/jentsch/2018/07/06/mid-season-woolly-apple-aphid-management-july-6th-2018/

Water management after shoot elongation has finished
The hot daytime temperatures, warm nights and abundance of moisture over the last month has contributed to the rapid growth of the corn crop. However, this growth won’t necessarily be mirrored in apples. Maize, grasses and a few species of broadleaf plants store energy by fixing carbon dioxide into four-carbon chains (dubbed C4 plants), which allows these plants to continue to produce sugars at night if appropriate heating units are meet and if they have adequate moisture. Apple trees are C3 plants, named after their three-carbon-long fixation process, and can only produce sugars during the daylight hours and when heat and moisture conditions favor photorespiration. Even if apples have slowed or stopped vegetative growth, the trees will need an adequate water supply to maintain tree health and fruit quality. NEWA offers an apple evapotranspiration and irrigation model that estimates water demand based on environmental conditions and planting density and age, http://newa.cornell.edu/index.php?page=apple-irrigation.

Single-site fungicide options for summer fruit rots
According to research from Dave Rosenberger, professor emeritus at Cornell University, bitter rot, white rot or black rot infections can occur early in the summer and lay latent until the fruit begins to ripen. Considering this, infections that are becoming visible now, and into harvest, may have occurred early in the season when insufficient fungicide residue was present during the infection period.

In our region, Honeycrisp is the most susceptible variety to bitter rot, and captan is often the primary fungicide used to protect against infection. Topsin (thiophanate-methyl) applied for sooty blotch and flyspeck does not control bitter rot. Captan applied alone (5 lb./A) or tank mixed with a strobilurin, e.g. Flint, Sovran, or SDHI fungicide e.g. Aprovia (benzovindiflupyr), Fontelis (penthiopyrad), are the most effective options. If a single-site fungicide is used to manage bitter rot, it is recommended to rotate mode of actions between applications to reduce the risk of the bitter rot pathogen developing resistance to a single mode of action. For more information on this nuanced approach to managing bitter rot visit: https://cpb-us-e1.wpmucdn.com/blogs.cornell.edu/dist/d/3767/files/2017/07/17-07-New-bitter-rot-control-strategies-sjjc9c.pdf.

Calcium timing and frequency to manage bitter pit
Bitter pit is a physiological disorder caused by low calcium (Ca) levels in the fruit. Susceptible varieties include Honeycrisp, Fuji, Jonagold, Cortland, Red Delicious, Golden Delicious. The majority of Ca is taken into the fruit from petal fall to the end of July. Calcium is relatively immobile within the tree and concentrations can vary between foliage, fruit and soil. Calcium levels and incidence of bitter pit are influenced by nutrient imbalances with nitrogen, potassium and boron, soil moisture levels, crop load and fruit size. An excess amount of magnesium or potassium will compete with Ca for uptake.

Light crops or excessive thinning can result in large fruit and Ca levels can often be diluted in large fruit. Calcium concentrations typically vary from stem to calyx end (location where bitter pit symptoms are most pronounced), excessively large fruit usually have exacerbated symptoms.

It is recommended to apply calcium sprays on a two-week interval beginning a week after petal fall and continue until harvest. Coverage is critical, since the Ca must contact fruit to be effective. During June-July it is recommended to apply 1-1.5 lb. of Ca/ acre, and 1.5-2 lb. Ca/ acre from August-September. Use caution when applying calcium if temperatures exceed 85°F to avoid phytotoxicity, especially if using calcium chloride.

San Jose scale second generation crawler emergence
To determine San Jose scale (SJS) development, continue to use 50°F as the low-temperature threshold for degree-day (DD) calculations and raise the upper developmental threshold to 91°F. After 700 DD, under these parameters, about 90% of first-generation crawlers will have hatched. Using the same model, second-generation crawlers will be about 15% hatched by 1400 DD. Growers should continue to refresh SJS tapes weekly to monitor crawler emergence.

Japanese beetles and orchard floor management
Japanese beetle (JPB) activity has intensified in some locations this year, compared to pressure observed in previous years. The last issue of WI Fruit News, https://fruit.wisc.edu/wp-content/uploads/sites/343/sites/36/2018/06/Wisconsin-Fruit-News-vol3-issue6FINAL.pdf, mentioned JPB females don’t like to lay eggs in grass over three inches long and grass that is kept a bit longer may help prevent some egg laying within the orchard. Therefore, close mowing of the alleyways should be avoided when Japanese beetles are active in the orchard.

Japanese beetle tend to have a strong preference towards Honeycrisp, but this year it appears that populations are more scattered through varieties. If populations are widely dispersed, it is advised to treat the entire orchard rather than making a targeted spray to the heavily infested blocks. Early signs of visible feeding damage warrants application of a repellent like neem or a full rate application of a Neonicotinoid, Assail (acetamiprid), Belay (clothianidin), Wrangler/Alias/Montana (imidacloprid). Note: Actara (thiamethoxam) is not as effective of a neonicotinoids as these other products. Where large aggregations are present and require immediate knockdown, options are limited and include BeetleGone (Bt), or Imidan (phosmet). If large aggregations of JPB are present in orchards, Assail will be the best alternative to organophosphates or synthetic pyrethroids.
Preparing soil for next year’s planting
The above average precipitation over the last several years, has resulted in many reports of tree deaths caused by soil-borne pathogens. Even if plant diagnostic labs detect evidence of or other pathogenic fungi in deceased samples, it’s hard to quantify if these pathogens directly caused the tree death. Varying organic matter and carbon levels in the soil have been found to modulate soil fungi activity. When preparing soil for next year’s planting, growers will typically correct soil pH, nitrogen, potassium and phosphorous levels, and other major macronutrients and micronutrients. Growers should also amend soil with a fixed carbon source such as compost, to reduce the likelihood of tree stress resulting in root infection by a soil pathogen. Research is showing that adding significant amounts of compost – about two tons per acre – will help suppress soil pathogens like Phytophthora or fusarium.

Powdery mildew
Orchards with powdery mildew infections will have terminals flagging with white and leathery mycelium on the growing shoots. In our region powdery mildew is not often a significant problem and temperatures around -15°F will kill the pathogen. In the southern United States powdery mildew can be quite severe and cause significant russeting. While this disease has thrived in this season’s warm weather, growth and spread stop when shoot elongation ceases. Once the shoot has set its terminal bud, powdery mildew growth will stop and the infected shoot will die. Rally or sulfur are good fungicide options to target PM by first cover. Growers can ensure an application was successful by the clean new tissue that should grow from shoots. Existing injury and visual symptoms from any infection will remain, even after fungicide treatments have been made.