During pruning this winter, there have been some reports of Japanese maple scale on apple trees. I have posted a photo of once such instance below, submitted in January by Extension agent, Tim Ohlwiler. Japanese scale has a broad host range and two generations per year in our area, and overwinters as immature 2nd instars. As with other scales, its management begins with an application of dormant oil (2-3%) prior to bud break in the spring, when temperatures are above about 55 F for 4 to 5 days. First generation crawlers should be targeted between mid-May and early June using 2% horticultural oil alone or at 0.5 – 1% in combination with Esteem or Centaur. Second generation crawlers should be targeted in early August, using the same products as for 1st generation. Researchers at the University of Maryland published a very informative fact sheet about Japanese scale biology and management that can be found at the following link.
Researchers from around our region are reporting much higher captures of brown marmorated stink bug (BMSB) in pheromone traps than have been recorded at this point in the season in recent years. Based on experience, we might expect BMSB numbers to increase over the next few weeks. Its feeding on tree fruits in August and September can result in substantial injury at harvest. Also, of course more adults can translate to higher numbers of BMSB invading homes and other buildings during their dispersal to overwintering sites between the latter portion of September through much of October. My post on August 11 included a table of insecticides that are considered effective against BMSB and a a reminder that scouting for BMSB injury (photos below) in apple orchards at this point might be most efficiently accomplished by examining fruit from the mid- and upper canopy of trees in border rows adjacent to woods; this is the “zone” where its injury at harvest has been most prevalent. I encourage growers to be vigilant in paying attention to this as the crop matures.
Brown marmorated stink bug (BMSB) pheromone traps are showing the presence of new adults and late instar nymphs that will soon molt to the adult stage. Captures vary among sites, but at some locations are considerable for this point in the season. These adults will produce another generation of nymphs that will become the adults that invade buildings in the fall when they seek overwintering sites. Nymphs are considered more susceptible to insecticides than adults, but older nymphs (3rd and 4th instars) can cause similar injury to fruit as adults. BMSB populations (based on captures in traps) are almost always highest between late August and early October, and feeding by BMSB during this period can cause considerable fruit injury and in some cases, injury to apples that is not apparent at harvest but is expressed after a period in post-harvest cold storage. Woodlands next orchards tend to be the “riskiest” borders in terms of BMSB prevalence, and injury to apples tends to be highest in fruit at the top and middle of trees in border rows next to woods. To gain a sense of BMSB injury at this point in the season, scouting could reasonably focus on fruit from these trees and canopy locations.
BMSB management options from this point forward are summarized in the table below. Because the residual efficacy of most insecticides against BMSB is fairly short, alternate-row-middle sprays against it at 7- to 10-day intervals are considered strongest. Note that many of the products listed below are pyrethroids or contain a pyrethroid; they and Lannate can cause secondary pests to flare.
With respect to codling moth (CM) and oriental fruit moth (OFM), management of third generation CM and fourth generation OFM occurs in August. The degree-day egg hatch models are not used to guide management for the final generation of these pests. Rather, pheromone trap-based thresholds can inform decisions about whether control is needed. Average captures (e.g. across 2 or more traps) per week of more than 5 CM per trap and more than 10 OFM per trap are considered to reflect a population that should be managed.
I’m having unexplained issues with updating my degree day graph for 3rd brood OFM, so today will just post by text. The optimal timing for the second half of third brood OFM larvae in APPLES is as follows: Assail at 2800 – 2900 DD; Altacor, Besiege, Delegate, Exirel, Imidan, Lannate, Verdepryn, or Voliam Flexi at 2900 – 3000 DD. In the Winchester area, we will reach 2800 DD on Aug 1-2, and 2900 DD on Aug 4-5.
On July 15, 2020 the EPA approved the renewal of a Section 18 Emergency Exemption for use of the neonicotinoid insecticide, dinotefuran, against brown marmorated stink bug in pome and stone fruit crops in Virginia. Growers from the other States that have previously participated in this Section 18 should contact their State Department of Agriculture regarding the status of this petition. The two products included in this exemption are Venom Insecticide and Scorpion 35SL Insecticide. Per application, Venom can be used at rates between 4.0 and 6.75 oz of product per acre (0.179 to 0.302 lb active ingredient) and Scorpion at 8.0 to 12.0 fl oz of product per acre (0.203 to 0.304 lb active ingredient). Restrictions include a maximum of two applications per season, a seasonal maximum of 0.608 lb active ingredient per acre (regardless of product used), and a minimum 7-day re-application interval. The re-entry interval for both products is 12-hours and a 3-day preharvest interval must be observed for both. This compound is highly toxic to bees and remains toxic to bees exposed to residues for more than 38 hours following an application. This Section 18 for use of dinotefuran in Virginia pome and stone fruit will expire on October 15, 2020.
In the attached graphs for CM degree day accumulation in central Virginia you will note that the last optimal timing for managing 2nd brood CM larvae using products indicated by the green lines is within the next 1-3 days, based on model predictions using a biofix of April 17 and 22 for the Red Hill and Batesville areas, respectively. After 2nd brood, the model is not used, so management decisions can be based on whether or not CM captures in pheromone traps exceed the threshold of an average of 5 moths/trap/week.