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Dogwood Borer and Scale: Not to be taken lightly.

Hudson Valley orchards vary in degrees of insect presence relative to last years management, proximately to woodland and abandoned orchard, levels of insecticide resistance, tree fruit varieties more or less prone to insect preference and a host of factors related to new invasives, weather, seasonality (and the list goes on). Although there are differences between orchard infestation, two insects stand out in my conversations with growers. It seems that everyone has one or both of these issues.

For this week, two pests should be on everyone’s radar: They are San Jose scale and dogwood borer. Before the season takes you by storm, you should strongly consider managing these pests if you have M-9 rootstock and or you have had even the slightest amount of SJS scale in your orchard at packout in 2014. Why…

San Jose scale on Empire

San Jose scale on Empire

If San Jose scale has been found at harvest, trees with infested fruit should, without question, be managed during this period to keep fruit from becoming over run a second year as significantly higher losses will occur.

Be mindful that a tree carrying a few SJS damaged fruit last season can become an eruption of fruit injury the following year if left unmanaged. To address the SJS issue, seasonal programs will require targeted applications of specific insecticides during three key periods of the season. Go back on your records, find the block, and hit it with everything you have. Simply, this insect has and will continue to cause sever losses in tree fruit due to lack of pre-bloom oil use (often due to the presence of Captan fungicide) and the industry loss of broad spectrum insecticides such as Penncap-M and post-bloom Lorsban.

San Jose scale Quadraspidiotus perniciosus (Comstock) (SJS): The SJS is now in the ‘Black Cap’ overwintering stage. The yellow females and males are beneath individual ‘scale’ coverings and will complete development, mate and bear live young or ‘crawlers’. They need to breath and metabolize food they obtain from feeding on the sap of the tree beneath their chitinous shell.

Pre-bloom (now) is by far the most opportune time to manage SJS. The overwintering immature stage, protected beneath the waxy covering are least protected from a spray application. However, developing foliage will increase ‘spray shadowing’ as the season progresses, reducing application effectiveness. A most effective timing during this period is delayed dormant, from the time silver tip begins to 1/2″ green. We are all familiar with the use of horticultural oil, Lorsban, Supracide directed against overwintered “black caps” during this period, as these are long-time standard control measures.

The use of these tools can suffocate the insect through the use of oil, or outright kill them through interrupting nervous system function (Lorsban & Supracide). The use of Esteem 35WP and Centaur provide control without the need for oil as a penetrant to inhibit SJS development. As we approach tight custer tree phenology the San Jose scale pest control options available to us are numerous, and to succeed, multiple strategies should be considered.

Pre-bloom options included:
* Lorsban & Supracide foliar application (DD_Pink)
* Esteem (DD-Pink)
* Centaur (DD-Pink)
* Oil (DD-Pink)

Post bloom 1st and 2nd crawler emergence options are:
* Movento SC (spirotetramat) PF-1C (2-3 weeks prior to crawler emergence)
* Contact insecticides at nymph emergence (pyrethroids, OP’s, Neonicotinoids and pre-mixed formulations)
* Esteem
* Centaur
* Oil

The Lorsban decision: A single yearly application of Lorsban (chlorpyrifos) can still be made to tree fruit. If chlorpyrifos (Lorsban or similar generics) is used in a pre-bloom foliar application, then it cannot be used in a post bloom trunk application. A pre-bloom chlorpyrifos application made at early pink will have a considerable impact on San Jose scale (SJS), rosy apple aphid (RAA), emerging obliquebanded leafroller larvae (OBLR), mullen and tarnish plant bug (MPB & TPB), European apple sawfly (EAS) and white apple leafhopper (WALH). Most importantly, if bees are brought into a block in a season of cooler temperature and delayed petal fall of later varieties, a pink application provides increased management of migrating plum curculio with less pressure to remove bees from a mixed block while active pollinators continue to work king flowers. It also provides a bit of insurance if beekeepers are delayed in removing hives from mixed variety blocks.

Be aware that the active ingredient in Lorsban and the Lorsban generics is chlorpyrifos, which has a high bee-poisoning hazard. Judicious use of this product, well before bloom, is essential to reduce the risk to active pollinators.

Remember, the earlier the application against the overwintering black cap phase, the greater the likelihood of success. Coverage is critical in scale management, requiring a slow travel speed (<2.5 MPH), low wind speed (<5 MPH) and as close to a dilute application as possible. Increased foliage equates to "shadowing" and reduced coverage, which of course is the essential control component against the overwintering life stage. Infestation levels that exceed just a few fruit at harvest in multiple blocks should be taken seriously. Even after a pre-bloom application is made, further management of populations should be considered as pockets of lingering scale in protected places are likely to remain in the tree canopy . SJS.female.2

As a follow-up to pre-bloom control of SJS, consider the use of Movento 240SC at 6-9 oz./A plus a non-ionic penetrant such as 0.25% to 1% agricultural oil or LI700 to address the San Jose Scale fruit injury at pack out last year. SJS on empire harvestThe active ingredient in Movento, spirotetramat, is taken into the foliage, systemically moving through plant tissue to stems, roots, and leaves to be fed upon by emerging SJS nymphs during emergence and feeding. Our research has found the single application of 9 oz./A at PF or two applications at 6 oz./A at PF and 2C will effectively control the 1st generation of the insect.

Softer insecticides, such as Esteem 35WP (pyriproxyfen) can be employed with or without oil, acting against the pest as an insect growth regulator (IGR), a unique mode of action for use against the immature scale. As the insect matures, the insecticide acts as a juvenile hormone analog to reduce the insect capacity to molt. Centaur 0.7WDG (buprofezin), also an IGR does require a penetrating non-ionic surfactant such as 0.25% v/v oil to be effective. Be aware that Movento (spirotetramat), a systemic insecticide, cannot be used pre-bloom as per label restrictions, as there is insufficient foliage for effective uptake. Movento has been found to be most effective after PF in one to two applications, requires a penetrating non-ionic surfactant. Incompatibility concerns over Captan use in early pest management programs for apple scab can be a formidable barrier when considering the use of oil. The possibility of phytotoxicity when using Captan near oil applications should be strongly considered when vying for a weather opportunity for SJS management windows.

Dogwood borer, Synanthedon scitula, (DWB): Is a common pest in the burr knots of apple trees on clonal rootstocks. The dwarfing rootstock, M.9, creates an abundance of burr knots. These root initials provide ideal locations for the dogwood borer to lay eggs and for larva to burrow and feed upon. Painting trunks can reduce the attractiveness of trunks to DWB but in most cases will not completely prevent infestations.

M.9 rootstock painted to reduce borer infestation

M.9 rootstock painted to reduce borer infestation

Prior to the adult emergence, DWB management could be employed using mating disruption. Research conducted by Art Agnell and Dave Kain has shown good results in NY using this approach . “Effective treatment with Isomate-LPTB dispensers at a rate of 100/A costs approximately $42/A ($40/100 dispensers)” can provide a good alternative or addition to trunk applications. “Assuming that efficacy of treatment with the pheromone is adequate, the ease of applying the pheromone dispensers, plus the fact that no special equipment is needed, and presumably its greater worker safety, may make this tactic attractive to growers looking for a good alternative approach.” Further information on dogwood borer mating disruption.

The G.11 rootstock produces fewer root initials, however, flaking bark on this rootstock can also act as a location for borers. Although there are fewer DWB in these varieties, they should not be overlooked during scouting as seen in this example.Various apple rootstock burrknot expression (under ‘Remarks column’).

Dogwood borer in M-9 plantings of high-density slender spindle blocks can cause considerable damage to young establishing trees. From our observations, DWB is very prevalent throughout many of the Eastern NY orchards with young plantings and can cause significant stress and losses if left unmanaged.

A directed, coarse, trunk spray of Lorsban to control the trunk borers should be considered in orchards employing dwarfing rootstock of apple such as M-9. In recent surveys throughout New York, dogwood borer, especially in Macoun, have been implicated in tree decline, often associated with phytophthora root, crown and collar rots. DWB and black stem borer, a newly emerging ambrosia beetle infesting trees undergoing excessive water stress, are often found together infesting the trunks of high density planting systems.

Further information on DWB Management.

Further information on dogwood borer mating disruption.