AppleTalk Conference Call Summary
Tuesday, June 13 2017, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments,
June 13th Call Stream: CLICK HERE
High heat and high humidity makes June the month for surprises
Check out these publications
• UW Fruit News, http://go.wisc.edu/143j34
• Cornell Scaffolds, http://www.scaffolds.entomology.cornell.edu/
• The Jentsch Lab, https://blogs.cornell.edu/jentsch/
Black and white rot
Black and white rot are fungi in the genus botryosphaeria that primarily affect woody plant tissue, and less commonly infect fruit. These two pathogens are ubiquitous and any place where you have deciduous trees around you, black and white rot can be found. These are weak pathogens and avoiding tree stress is the best way to mitigate against the risk of infections. These diseases do have a period of time when they are sporulating. There are no spores October through April, but June is the peak time for black rot spread. Generally, we need a trauma event to allow the pathogen in, e.g., pruning cut or limb breakage or fire blight canker. Trauma stress is the key to focus on, rather than water or heat stress, to mitigate against an infection. Summer applications of captan is the primary way to protect against infection. Considering the risk of infections from black rot and fire blight, this would be a good time to avoid summer pruning.
Organic growers applying compost teas or plant-host resistance inducers, which could offer some protection against black and white rot, should avoid applications of sulfur, since the sulfur may reduce the efficacy of these bio-rational fungicides. Trees with black rot infections can be managed for the long term, especially once trees are several years old. Young trees are more susceptible to black rot and less able to fight off infection. Larger trees most likely have reduced susceptibility.
Bitter rot
Bitter rot often becomes a problem later in the summer, however if extreme heat and humidity persist, it may become a problem earlier in the season. Bitter rot can be very devastating because it can spread from fruit to fruit. Captan is also one of our best options to protect against bitter rot. The greater the amount of relative humidity and heat we have, the greater the amount of pressure we can expect from bitter rot.
Sooty blotch and flyspeck (SBFS)
We will talk about SBFS in greater detail next week. Right now SBFS are sporulating off their wild hosts of brambles, which surround orchards. If you go to these brambles, scout for black specks on canes of brambles, which are likely to be the apothecia (fruiting body) of this fungi.
Apple scab
We are well past primary scab season and secondary scab infections are releasing millions of conidia during periods of high heat and rain. Young tissue on trees remains highly susceptible to scab and just because it is hot, apple scab can remain a persistent problem. If you have no scab, intervals between sprays may be stretched and rates can be adjusted, but need to consider that protecting tissue from black rot and white rot would still warrant applications of captan.
Fire blight
Fire blight remains a major concern in many orchards, however, at this stage, we need to have inoculum already present in the orchard to have problems. Continue to scout for shoot-blight symptoms, which can spread from branch to branch and potentially tree to tree during storms. Depending on when shoot blight shows up, the following options may be considered:
1. Apogee applications may still have some utility. Most trees are still growing and elongating shoots and could expect to get some shut down of shoot growth, if applications are made soon.
2. Prune and remove shoot strikes. Need to be cautious about this practice and make sure it is fire blight before aggressively pruning.
3. Copper may be applied to limit the spread. Not going to prevent growth of infection within the tree, but can help prevent spread to other trees. Use very low rates, or copper soaps. Do not want to do this to mature trees with a full crop. Long days and sun intensity can also cause sunburn on fruit. Do not compound this by applying something phytotoxic like copper on fruit.
Trauma blight refers to fire blight infections that spread after hail or high winds damage young tissues in trees. Inoculum is needed to be in the orchard already to have a fire blight infection after a trauma event. A fire blight free orchard, should not be at risk of having to make an application of strep. Tank mixes of Regalia plus strep or Regalia, strep + Regulaid may offer some additional rescue protection. Regalia is locally systemic or translaminar and may be aided in using a penetrant. Research suggests that streptomycin needs to be applied within 24 hours of a trauma event to have any benefit. We want to avoid applying streptomycin in the summertime, unless there is an absolute need. Young trees, less than three years old or high-density plantings, are at the greatest risk of fire blight. Copper applications will not eradicate fire blight that has already infected a tree, but can reduce the spread to other trees.
Question: when is it too hot to spray?
• Most materials we are using are not negatively affected by fast drying conditions.
• With high pressures and small droplet sizes, we do run the risk of a spray evaporating and pesticide will volatilize before it hits the tree.
• Most surfactants used as adjuvants and not labeled as a penetrant, high temperatures should not cause a problem.
• Staying away from Regulaid and LI 700 under high temperatures may be a good idea.
How do we manage scab with the pop-up showers that drop over two inches of rain?
The amount of scab inoculum present in the orchard plays a role in how much it could have spread scab. Maintaining low rates of captan on a more frequent spray schedule is an option where rains are frequent and consistent. This method would require you reapply captan at 2-3 lb. rates before every rain, rather than 5 lb. rates on an extended spray schedule.
Miscellaneous musings on our favorite June insect pests
European red mites (ERM), have a higher development threshold than many insects which normally use 86°F as the upper limit of their development. Therefore, ERM will not be slowed down by high heat, in fact their growth can outgrow and out populate their predators. Most of the predators we have in the orchards cannot reproduce as fast as the ERM.
San Jose scale crawlers are active. In last week’s AppleTalk post we discussed extensive management and monitoring options. If you suspect scale, because you had lots of red dots with a white ring around your fruit at harvest, monitoring tape should be hung now.
Obliquebanded leafroller (OBLR) flight has begun and traps should be hung. When diamides, spinosads or Bt products are used for codling moth management, OBLR is rarely a concern. However, in orchards treating codling moth with mating disruption, neonicotinoids, codling moth virus, extra attention will need to be paid to the summer generations of OBLR.
Plum curculio just won’t back down this season and some growers are still reporting fresh oviposition scars on the edge of blocks. CORRECTION, when checking for new PC scars, if the orchard was sprayed with surround, this is not killing the females. If perimeter sprays were made, be certain to scout the area of the orchard that did not receive insecticide treatment. Anything that has not been sprayed is fair game for PC.
Codling moth (CM) – We often talk about CM in extreme and hard rain events causing a negative impact on egg hatch. If the larva has to travel a foot or two to find a fruit, the likely hood is it will not survive a two inch thunderstorm and will actually drown, according to Larry Gut. It is essential we pay attention to the CM that flew 250-350 DD prior. If you are catching high counts now, these will not be treated for at least another 250 DD. When determining the need to retreat, take a look at what the flight was like 250-350 DD ago and just know the drowning codling moth larva is the silver lining to any scab that spreads during these rainstorms.
Apple maggot (AM)
Apple maggot have been caught as early as June 15 in some years. If you have had issues with AM or have early ripening cultivars, e.g., Lodi, yellow boards or red spheres for AM monitoring can begin to be deployed. Yellow boards can provide an early warning system by attracting AM during their feeding period. If bait is used in addition to visual traps replace volatile lures according to the manufacturer’s directions, e.g., seven to ten days. It is advised to set up a minimum of three traps per ten acres at the beginning of July; trap density should gradually increase to one trap every 200-300 feet along the orchard perimeter, as the season progresses. Locate traps along perimeter where wild hosts are present and near early ripening cultivars. Hang traps at eye level, and make sure they are visible. Traps can be placed in early-season varieties that exist on the interior of block, since the trees can harbor resident populations that may not affect neighboring varieties.
