The treatments at ranch 1 were applied during the winter, which in Ventura county is marked by cool ambient temperatures , lower average relative humidity, and increased chance of rain and clouds. In contrast, ambient conditions at the end of summer when treatments were applied at ranch 2 are marked by warm temperatures , consistently moderate relative humidity , no rain, little cloud cover, and calm winds. Actual conditions during 2018 generally reflected these long-term averages. Ambient temperature was generally lower during the ranch 1 experiments compared to the ranch 2 experimental period after treatment application . Relative humidity was much lower for ranch 1 compared to ranch 2 between about 30 and 10 days before treatment application, but was not different between the ranches on the day of treatment application or after. A total of 2.6 cm rain over two days fell in the area within one week of treatment application at ranch 1. There are two possible ways that ambient weather conditions differentially influenced cane Botrytis development between the ranches. One way is that the favorability to disease development of ambient weather conditions may combine with other factors, such as wounding, to influence colonization and symptom expression. However, conditions were slightly more favorable for ranch 1 after treatments were applied due to lower temperatures and rain, therefore wounding from leaf removal treatments would have been expected to increase disease severity. Another way is that the higher relative humidity before treatment application at ranch 2 could have led to higher levels of inoculum present in the environment, which in turn could lead to higher disease. Thirdly, conditions for ranch 2 may have been more favorable for infection on the days of treatments application and shortly afterward. While relative humidity, round plastic plant pot daily maximum temperature, precipitation, and wind were similar between the two ranches, daily minimum temperature was higher by about 10o C at ranch 2.

If it is assumed that the optimal temperature of 20°C for infection of strawberry flowers also applies to raspberry canes, then conditions at ranch 2 were more favorable than ranch 1 inthe days after treatment application, which could have led to higher incidence of cane Botrytis. We hypothesized the removal of lower leaves would shift environmental conditions within the canopy to be less favorable for cane Botrytis development. Unexpectedly, in our study leaf removal treatments appeared to increase relative humidity within the raspberry canopy, especially within dense plantings. However, this effect was not consistent across experiments. In Northwest Washington, minimum air temperature, night air temperature, cumulative rain, leaf wetness, and duration of leaf wetness was correlated with B. cinerea colonization of processing raspberry fruit . In strawberry, incidence of flower infections by B. cinerea has been reported to be correlated at relative humidity >80% and >90% . Given that leaf wetness typically forms at night and that leaf wetness is important in development of many diseases caused by B. cinerea, we would expect disease to be more severe in 3-row treatments that had higher relative humidity at night. In our study, however, relative humidity was higher at night for only two of the treatments at ranch 2 but disease was more severe compared to the control for all three treatments. Therefore, relative humidity may not be a significant factor for cane Botrytis severity. Leaf removal treatments also influenced temperature, but the effect was more consistent than relative humidity across experiments. Temperature was higher in treated canopies than the control during the day but were lower than the control at night. This suggests that the leaves in the raspberry canopy serve to moderate temperatures, or reduce variability, with respect to daily fluctuations in ambient temperature. This assertion is supported by the generally greater time per day of significant change from control in manual treatments, given that the manual treatment removed the most material from the lower canopy. Because the effect was generally consistent across experiments and treatments yet few significant differences in disease incidence were observed, the influence of canopy on temperature is may not an important factor for cane Botrytis incidence.

We found few significant differences in cane Botrytis incidence among treatments despite finding a strong influence of leaf removal on disease severity. However, a non-significant trend of higher incidence in the manual and twine treatments versus blade removal and the control was observed in all three experiments on the first rating date. Because the manual and twine treatments removed petioles from the cane whereas petioles remained attached to the cane in the control and blade treatments, the wounding caused by petiole removal may increases disease incidence early in the season. By the last rating date, however, this trend had dissipated or reversed at ranch 1, but remained a trend at ranch 2, especially between the blade and twine treatments. Taken together, this suggests leaf removal treatments may have an impact on disease incidence right after leaf removal or early in the season but that the impact may diminish as the season progresses. Furthermore, the length of time the trend was observed supports our suggestion above that the cultivars used in our experiment differ in susceptibility or response to wounding. While this suggests that primocane yield is not influenced by cane Botrytis, itis unknown if receptacle counts are representative of marketable yield. Even if actual marketable fruit could have been collected, collecting yield data from small plots of raspberry is known to be logistically challenging and may not be a reliable measure of yield or representative of the potential raspberry yield. Though there were many infected canes that developed sclerotia near the end of each experiment, the impact of the sclerotia on the floricane is unknown. Additional studies are needed to understand the effects of sclerotia on bud break and bud elongation in fresh market raspberry. Because we did not perform a true replication of any of our experimental conditions, future research is needed to confirm the influence of leaf removal on incidence and severity of cane Botrytis in different production conditions. Currently, in California fresh market raspberry production there are no management practices commonly used to manage cane Botrytis.

The twine treatment is the current experimental method of leaf removal practiced by growers in Ventura County due to its labor efficiency. Because it is an aggressive practice, we hypothesized that a practice that causes less wounding would improve cane Botrytis management. The method we examined was the manual removal treatment, which was designed as an equivalent canopy treatment but with less wounding. Across all three experiments there were no significant differences in cane Botrytis severity between the twine and manual treatments. The use of high powered blowers to remove leaves in the lower raspberry canopy would be beneficial to evaluate for novel management practices of cane Botrytis. Our study indicates that wounding by twine leaf removal is not important for disease severity. Our experiments have shown leaf removal methods can be applied for certain cultivars and row spacings.California agriculture is in a time of opportunity to adopt sustainable practices for the management of challenging issues such as soilborne disease. In the previous decades, soilborne diseases were commonly managed with the use of chemical fumigation, 25 liter round pot but the widening restrictions on the use of fumigants in the San Joaquin Valley of California has posed a challenge for growers. One of the affected crops in California is processing tomato , which averaged 1.1 billion dollars in value from 2013 to 2017, and accounted for 93% of the production in the United States in 2017 . Despite the total value of processing tomato statewide, growers face challenges due to the low market return on a per area basis. Southern blight is a disease of processing tomato that has long been an economic concern in the San Joaquin Valley, and recently caused a widespread epidemic in both the San Joaquin and Sacramento Valleys . The threat of southern blight has caused reductions in acres planted with processing tomato in the southern San Joaquin Valley . Southern blight is caused by the soilborne fungus Athelia rolfsii C.C. Tu & Kimbr. that has a host range of over 500 different plant species . The fungus produces a white, typically fan-shaped mycelial mat and distinctive tan to reddish brown sclerotia with walls are composed of chitin and laminarin . The sclerotia survive and germinate at soil depths of 0 to 8 cm and are commonly dispersed by the movement of infested soil or plant material . Initial infections in the field most commonly occur on plant tissues that are in contact with the soil surface where sclerotia are stimulated to germinate by drying and remoistening . Following germination from sclerotia, mycelia of A. rolfsii colonizes aboveground plant tissue and releases cell wall degrading enzymes. The enzymes disintegrate host tissues and when colonizing stem tissue form a lesion around the stem near the soil line that advances rapidly to the point of girdling the stem . The pathogen is most damaging when it infects stems or crowns, in which it causes wilting, cankers, rot, or whole-plant necrosis on various crops . In processing tomato, the most common symptom of southern blight is rapid wilt of vegetation above the ground. The temperature range for mycelial growth is from 8 to 40ºC, and the optimal temperatures for sclerotia formation is from 27 to 30ºC . Overall, temperatures 25 to 35o C are most conducive to disease development . Sclerotia form on mycelial mats that are 5 to 6 days old . When mature, sclerotia can persist in the soil for many years . Additionally, A. rolfsii can persist in the soil saprophytically as mycelium on plant debris . If management practices are not adopted, within a season or two a single infected plant can produce thousands of sclerotia, potentially resulting in serious yield loss due to southern Blight . There are several methods to reduce losses caused by A. rolfsii, but their uses are limited in processing tomato production in California.

These include rotation with nonhost crops, minimizing soil moisture on the soil surface, and deep plowing to bury the sclerotia. Rotating with crops that are non-hosts including corn, barley, wheat, and small grains has been shown to reduce sclerotia density in subsequent years . However, these rotation crops are not economically viable as regular rotation partners in the San Joaquin Valley of California, and few alternatives are available due to the wide host range of the pathogen. Although reducing soil moisture has been shown to reduce southern blight , the use of subsurface drip irrigation has already become the standard practice in California. The drip lines are buried at a depth of 25.4 cm to 30.48 cm for weed management, water efficiency, and to reduce A. rolfsii inoculum accumulating in the furrow . Athelia rolfsii sclerotia cannot survive long periods under anaerobic conditions, thus deep plowing of infected plant tissue and sclerotia to at least 20 cm depth has shown to reduce inoculum . However, this approach is not feasible in California production systems because the drip lines remain buried for two to three consecutive crop seasons and could be subject to damage from deep plowing. Taken together, agronomic methods have little potential to further improve the management of southern blight.Fumigation with metam sodium or metam potassium was traditionally relied upon to effectively manage A. rolfsii in processing tomato in the San Joaquin Valley. For effective control the product must be applied through sprinklers, however, sprinkler application is restricted. The alternative method to sprinkler application is shanking the product into the soil, but this approach does not allow for effective dispersion of metam sodium into the soil, therefore it is not effective . There are effective fungicides such as flutolanil, penthiopyrad, and tebuconazole available to manage southern blight in vegetable crops . However, processing tomato cultivars are determinant, not trellised, and the canopy is often full late in the season when the pathogen is most active. These characteristics prevent chemical application to the vulnerable stem tissue at or above the soil line and is the main reason why chemical management of southern blight has proven ineffective in processing tomato . The processing tomato industry in the San Joaquin Valley of California would benefit from having new efficient and sustainable approaches to manage southern blight.