Two-spotted Mite 



Two-spotted mites provided a very interesting case 

 for the strawberry IPM program this year. Late in the 

 1987 season, strawberry growers saw the removal of 

 cyhexetin (Plictran^'^) from use for mite control. This 

 loss left very few materials available to growers. Mite 

 infestations were early and heavy in some locations in 

 1988. Ordinarily, high mite levels do not occur before 

 mid-June. This time is approaching hai-vest which 

 makes spraying difficult due to harvest intei'val restric- 

 tions. This year, with such high levels early in the 

 season, gi-owers were concerned. The use of predators 

 for the control of two-spotted mites has been studied 

 (Croft et al., 1976; Penman et al., 1979; Waite, 1988). 

 These predators feed on all stages of two-spotted mite, 

 disperse rapidly in strawberry fields, and are indige- 

 nous to the Northeast. In many cases, the natural 



Table 1. Two-spotted spider mite populations per 

 strawberiy leaf at first occurrence of the predator 

 mite Am6/ys/ews/a//ads, and for 3 weeks following 

 its appearance. No miticide applications were 

 made. 



Average TSM population per leaf 



Grower Weeks after 1st occurrence of A fallacis 

 site 12 3 



1 

 2 

 3 

 4 

 5 

 6 

 7 

 8 



Mean 



7.8 



6.6 



11.2 



0.9 



populations are sufficient and appeared to be effective 

 in keeping two-spotted mite population levels low. 

 Releases of artificially reared populations can also be 

 made in locations where the natural populations are 

 insufficient for control. A local business, Biokon, has 

 emerged for the distribution of the predator Ambly- 

 sieus fallacis. In cooperation with Biokon, the straw- 

 berry IPM program monitored population levels of pest 

 and predator mites prior to and after releases of the 

 predators were made. The results were impressive. In 

 most cases the predators "cleaned up" the two-spotted 

 mites within 2 to 3 weeks, a result difficult to achieve 



Table 2. Mean numbers of fungicide applications 

 and percent injured fruit at harvest for IPM and 

 non-IPM blocks in 1988. 



Number of fungicide Injured fruit 

 Treatment applications at harvest (%) 



IPM 

 Non-IPM 



1.1 b- 

 3.8 a 



5.6 a 

 6.3 a 



•Means within columns not followed by the same 

 letter are significantly different at odds of 20 to 1. 



with miticide applications. Data in Table 1 illustrate 

 these results. 



Botrytis Gray Mold 



Strawberry growers make more pesticide applica- 

 tions to control Botrytis cinerca, the fungus which 

 causes gray mold, than for any other single problem in 

 commercial strawberiy production in Massachusetts 

 (Schloemann and Cooley, 1987). In 1987 Massachu- 

 setts growers applied an average of 5.6 fungicide 

 sprays, ranging from to 15. These applications cost 

 growers about $140 per acre. Studies have shown that 

 the most susceptible gi-owth stage for the infection of 

 Botrytis is bloom, when the fungus infects the tender 

 blossom tissue (Devaux, 1987; Grove etal., 1985). The 

 infection remains latent until conditions of fruit devel- 

 opment and favorable weather conditions coincide. 

 Therefore, the IPM program in Massachusetts targets 

 bloom to prevent infection. Many growers have had 

 great success with this program of bloom sprays and 

 have saved several spray applications later in the sea- 

 son. Table 2 shows that under IPM recommendations 

 in 1988, cooperating growers made an average of 1.1 

 fungicide applications this year, compared to 3.8 in 

 non-IPM blocks on the same farms, a 70% savings. 

 Incidence of Botrytis in IPM vs. non-IPM fields was not 

 significantly different. However, disease pressure was 

 light this year. The progi-am's goal is to keep Botiylis 

 sprays to an average of 3 or less. 



Inoculum causing blossom infections comes from 

 ovei^wintering Botiytis in the live leaf tissue of straw- 

 berries protected under the mulch (Braun and Sutton, 

 1986; Braun and Sutton, 1987; Sutton and Braun, 

 1987; Sutton, 1988). These leaves are infected in the 

 fall. As they senesce in the spring, they produce spores. 

 Efforts are undei-way to develop ways to inhibit the 

 ability of Botrytis spores to penetrate the leaf surface 

 successfully in the fall, thereby reducing the initial 



14 



Fruit Notes, Spring, 1989 



