-28- 

 surface. A minimum spray schedule involves 3 applications, one at 10% bloom, one 

 at 50% bloom and one at tiie end of bloom. Where gray mold has historically been 

 a problem, applications should start at white bud, then the 3 bloom applications should 

 be made, and then applications should be made during fruit development at 5 to 10 

 day intervals. To maximize the protection it is wise to time spraying according to 

 plant development and weather. Rapid plant growth leaves tissue unprotected until 

 the next application, and heavy rain for more than 24 hours washes fungicides off 

 and provides an excellent infection environment. Therefore, in addition to the 

 prescribed applications, additional sprays should be made after 24 hours if rainy periods 

 occur. 



Such intensive fungicide spraying can and has led to resistance to some chemicals. 

 Specifically, the systemmic fungicides, benomyl (Benlate®), thiophanate-methyl (Topsin 

 M®) and vinclozolin (Ronilan®) can become ineffective if used alone or too heavily. 

 The broad-spectrum contact fungicides, captan and thiram, are not likely to produce 

 the same problems. As a consequence Benlate®, Topsin-M® or Ronilan® should be 

 used in combination with a half-rate of captan. This reduces the risk of resistant 

 Botrytis developing, while enabling growers to use one of three very effective 

 chemicals. The rates for these chemicals are given in 'Managing Diseases and Insects 

 on Small Fruits in New England', available from the Massachusetts Extension Service, 

 Cottage A, University of Massachusetts, Amherst 01003. 



There is another problem with the systemic fungicides in that they do not control 

 Rhizoctonia , Phytophthora , Rhizopus and Mucor , fungi which also cause berry rots. 

 In some cases, post-harvest rots caused by Rhizopus and Phytophthora have actually 

 increased where Benlate or Ronilan were the only fungicides used. 



Cultural practices can reduce the amount of inoculum which contacts plants, 

 and reduce the free moisture on plants necessary for infection. Mulching with straw 

 or plastic keeps berries from contacting soil, hence reducing inoculum pressure and 

 improves fungicide coverage. Narrower rows promote air circulation and drying, 

 minimal weeds accomplishes similar goals. There is some evidence that adding 

 micronutrients may decrease gray mold, though the interaction of nutrition and the 

 disease has not received much study. 



Some cultivars are more resistant to gray mold than others. In general, berries 

 which are firmer are more resistant. A recent study at Cornell rated the following 

 cultivars in decreasing order of susceptibility to berry rots: Honeoye, Guardian, 

 Canoga, Tenira, Surecrop, Holiday, Veestar, Vibrant and Earlidawn. Of these, the 

 first three cultivars were significantly more resistant than the others. Plant breeders 

 are continuing to develop gray mold resistant cultivars. 



Finally, an experimental approach to control has been tried using the biological 

 control fungus Trichoderma . Preliminary results were not as consistent as control 

 achieved by fungicides, but Trichoderma may yet be developed into an effective 

 alternative to fungicide control. In the future, it may be possible to reduce or eliminate 

 fungicides by using a combination of resistant cultivars, biological control agents 

 and careful management of horticultural practices. 



Obviously, these measures are aimed at reducing field incidence of gray mold. 

 These practices will, as a consequence, reduce post-harvest disease incidence. 

 Refrigeration is an option most small growers use to further reduce post-harvest 

 gray mold. Beyond one or two days after harvest, strawberries become increasingly 

 susceptible to rot, and the best strategy is to use or process them as soon as possible 

 after harvest. 



Acknowledgment: Special thanks to Paula Saucier for the illustration. 



