When strawberry plants are grown under relatively low night humidity (in dry climate or in an intensively heated greenhouse at night), tipburn and calyx burn may become problematic. Tipburn is a localized calcium deficiency that is typically initiated in the fast growing shoot tip. The symptom may be first noticed as a darker-colored shoot tip, which later develops a necrotic distal end of leaf or calyx. Calyx burn is particularly problematic as it reduces cosmetic (visual) quality of strawberry fruit.
The localized calcium deficiency is often caused by limited allocation of calcium driven by mass flow (transpiration). In crops like lettuce, tipburn can be mitigated by increasing transpiration rate during the daytime. In strawberry, however, more effective way to mitigate tipburn is not via increasing daytime transpiration but suppressing non-stomatal transpiration during the nighttime. Incidence of tipburn and calyx burn in strawberry can be reduced by lowering nighttime VPD (or increasing relative humidity) in the greenhouse.
Guttation and tipburn. Guttation is a good indicator of plant health in strawberry. Guttation occurs when the xylem pressure is high with all stomates closed and little non-stomatal transpiration under humid night condition (>95% at 15C or 0.1 kPa VPD). Guttation and tipburn incidence are known to be correlated. When plants are grown under conditions where guttation is rarely seen, these plants typically exhibit tipburn.
Under-bench misting system. For this reason, we started using below-trough misting to achieve 95% relative humidity at plant level for a minimum of 3 hours per night. This has been done by intermittently operating the misting system with blowers to enhance evaporation. Wetting plants directly by misting should be avoided as it would increase the fungal disease incidence. As soon as 3 hours of high humidity are achieved, moisture can be released from the greenhouse to lower the humidity. Most cultivars do not seem to require this high humidity hours every night but some cultivars (e.g., Tochiotome) tends to be sensitive to tipburn inducing conditions and require more hours of high humidity every night.
Ca supplementation. While tip/calyx burn is a calcium deficiency, there is often sufficient amount of calcium in the root zone. Therefore, simply increasing calcium concentration in the nutrient solution does not solve the problem. A typical solution that growers attempt is a foliar calcium supply. It is recommended that applications should cover all shoot tips and growing leaves, not symptomatic leaves and calyx (because they are irreversible). The impact of foliar calcium application seems to be inconsistent, and also keeping plants wet all the time is the general concern of potential disease outbreak. For this reason, we usually recommend the nighttime humidity management as a most effective method to mitigate tipburn.
More information on this topic:
Kubota, C. and M. Kroggel. 2012. Soilless strawberry production in semiarid climate: Improving fruit quality by nighttime VPD control. Poster presented at 2012 Annual Conference, July 31- August 3, 2012, Miami, FL.
Kroggel, M. and C. Kubota. 2017. Controlled environment strategies for tipburn management in greenhouse strawberry production. Acta Horticulturae 1156:529-536.
Kubota, C. 2019. Understanding crop responses to controlled climates in greenhouses. Chapter 7. (P.205-223) In: (L.F.M. Marcelis and E. Heuvelink eds.) Achieving sustainable greenhouse cultivation. Burleigh Dodds Science, Cambridge, UK.