A Question of Scale
Reprinted from Scaffolds Fruit Journal, Vol. 14, No. 4.
Dick Straub, Harvey Reissig & Peter Jentsch, Cornell University, New York State Agricultural Experiment Station
According to grower reports, San Jose scale is again gaining ground in many orchards throughout the state. This pest can seriously affect fruit quality and, if unmanaged for a number of seasons, can result in poor tree health, or even death. We
are fortunate to have a list of efficacious treatments that can be employed at various windows during the season [Editorial note: See http://www.umass.edu/fruitadvisor/NEAPMG/index.htm]. In the universal language of spraying apples, however, good coverage is necessary for control of scale.
Treatment periods 1 and 2
(green-tip and half-inch green). Oil, Lorsban and Supracide directed against overwintered 'black caps' are long-time standards, and each still has a place in control programs. Treatment during one or both of these time periods represents a first line of defense against scale. In most instances, applications at both green tip and half-inch green are probably unnecessary, but at this busy and often inclement time of season, an option should be welcome. Oil + Lorsban tank-mixed is a traditional treatment. Historical evidence and recent results by Harvey Reissig & Combs (2003) suggest that there is not much synergism in the combination, i.e., either oil alone or Lorsban alone perform just as well. Many growers favor the combination, however, believing that it increases the efficacy against overwintered OBLR larvae - this is probably true.
Treatment periods 3 and 4
(crawlers of the 1st and 2nd generations). Relatively new on the scene are Provado, Esteem and Assail. Quite frankly, we have very little experience with Provado against this pest, but it may be worth a try if other susceptible insect species are present during recommended treatment periods. Esteem is an insect growth regulator that functions as a juvenile hormone mimic and thereby inhibits metamorphosis from one stage to another. It is most effective when directed against crawlers -- preferably at first appearance. Esteem has no contact toxicity and tends to act very slowly. Assail is a new-generation broad-spectrum neonicotinoid that, somewhat similar to Esteem, is most effective when directed against crawlers at first appearance. Esteem and Assail are also effective when applied at half-inch green (Reissig & Combs 2003), but such usage is less economical than other options during this treatment period. Although the efficacy of both materials is improved by the addition of oil, these tank-mixes may be phytotoxic and result in fruit finish problems.
Treatments to be applied at the first appearance of summer brood crawlers are best timed by the use of a degree day model (1st generation, 500 DD50 from 1 March; 2nd generation, 1451 DD50 from 1 March) [Editorial Note: See http://www.caes.state.ct.us/Weather/GDD/GDD.htm for CT degree day information]. Because each generation of crawlers emerges over an extended period of time (Note: San Jose Scale females do not lay eggs, but rather give birth to live young), for complete control a second application 14 days later is advised. Correct timing of treatments is critical with Esteem and Assail, and calendar dates are generally too imprecise to be of benefit. For example, Table 1 shows that on average, 1st appearance of crawlers occurs approximately 21 days after petal fall. Also evident, however, is the extreme variation, i.e., the 500 DD event at the Hudson Valley Lab during the last decade has occurred at