such as rotting and leaf-spotting appear. The gray, 

 fuzzy areas actually are masses of spores. These 

 spores infect young tissue, and the new infections 

 remain dormant until the tissue is fully mature. 



Most of the important fruit infections occur at 

 bloom. Spores from decaying leaves infect flower 

 petals. If conditions are wet, these infections may 

 kill the flowers or the new developing fruit. Under 

 normal conditions, the infections remain dormant in 

 the fruit, and when the fruit become ripe, infections 

 grow rapidly. Infections can spread rapidly from 

 infected fruit to nearby uninfected fruit. Again, the 

 more moisture, the faster the spread. After the 

 strawberry is done fruiting, the fungus infects new 

 leaves on the plant throughout the summer. The 

 fungus then overwinters in infected but apparently 

 healthy leaves. These leaves produce spores the 

 following spring, and the cycle repeats. 



Management. How does this information sug- 

 gest that we should manage the disease? We real- 

 ized immediately that growers were concentrating 

 at least half of their fungicide applications on the 

 ripening berries. This situation was bad from two 

 points of view. First, most of the infections had 

 already occurred and were in the berries. Second, 

 the fungicide residue was being left on the fruit 

 which consumers were going to harvest and eat. 



Our management technique sought to break the 

 Botrytis life cycle. As a first step, we aimed to protect 

 blossoms from infection, rather than the berries. 

 Our recommendation was to apply a fungicide up to 

 3 times during bloom. In many years, a single early- 

 bloom application will protect fruit. If more than 1 

 application is used, we recommended that they be 

 spread about 7 days apart. Later we modified this 

 recommendation, suggesting making the first appli- 

 cation at 10% bloom, the second at mid-bloom, and 

 the final application when bloom was about 90% 

 done. 



The cycle can also be broken in fall or early 

 spring. Benlate™ or Topsin-M™ plus captan or 

 thiram applied once late in the growing season 

 (September or October) will also reduce overwinter- 

 ing inoculum. However, Benlate and Topsin-M may 

 be toxic to some mite predators in strawberries, and 

 may hurt attempts atmite biocontrol. Alternatively, 

 Ronilan™, while more expensive, may be combined 

 with captan or thiram and used to reduce the over- 

 wintering inoculum. The same treatment may be 

 useful in spring. In some cases, this single applica- 

 tion in combination with "clean" cultural practices 

 will be sufficient to remedy a building gray mold 

 problem, and eliminate the need for more sprays. 



Cultural practices can play an important role in 



managing gray mold. Narrow plant rows and wide 

 spacing between rows will allow greater air circula- 

 tion, better drying, and better pesticide coverage. 

 Rapid drying of foliage, blossoms, and fruit during 

 periods of high humidity, rain, irrigation, or dew will 

 decrease the chance of Botrytis spores germinating 

 on plant surfaces. Beds that become too crowded are 

 likely to promote Botrytis fruit rot. So, "clean" 

 cultural practices mean keeping weeds down and 

 keeping plant rows aerated. In the future, it may 

 mean literally cleaning out the old, dead leaves in 

 the planting. 



What we have done in developing IPM for Bot- 

 rytis is substitute phenological monitoring for pa- 

 thogen monitoring. We know that the plant and 

 pathogen evolved together. The pathogen is ready to 

 infect the host plant when conditions are optimum 

 for the pathogen's survival. Both the plant and 

 pathogen develop in response to the same stimuli, 

 which generally are temperature and moisture. By 

 watching plant development, fungicides which pro- 

 tect the plant and destroy the pathogen can be timed 

 well. It is not quite as accurate as watching the 

 pathogen directly, but it is infinitely easier. 



Since temperature and moisture both pro- 

 foundly affect the pathogen, we might also monitor 

 these variables. Mike Ellis has developed a model 

 and it may allow us to refine this recommendation, 

 and apply fungicides in response to measured infec- 

 tion periods. 



Mite IPM 



Two-spotted mite (TSM) feeding in small fruit 

 crops results in yield loss and a reduction in plant 

 vigor (Oatman et al., 1981). Few miticides are 

 labeled for strawberries, making an alternative 

 method of mite control critical. Further, resistance 

 to miticides is common and jeopardizes their future 

 utility (Gould, 1973). We knew of the effectiveness 

 of the predatory mite Amblyseius fallacis in control- 

 ling TSM populations in various crops including 

 strawberries (Croft and Hoyt, 1983). 



Soon after the Massachusetts IPM program 

 started, we were faced with a severe problem in 

 dealing with mites. Chemical miticides were either 

 ineffective or were withdrawn from the market. 

 Growers had no alternative but to try biological 

 control. We assisted growers with the introduction 

 of mite predators, Amblyseius fallacis (Biokon In- 

 sectaries, 34 Bay Rd., Belchertown, MA 01007, other 

 companies also rear mite predators). Additionally, 

 we recommended that growers refrain from using 

 Benlate, Topsin-M, or Lorsban™, since these mate- 



Fruit Notes, Spring, 1991 



