Page 9 - Griffin Gazette Issue 3 - 2022

Tip burn is a physiological disorder that affects many But what causes root pressure, and why would perfectly
crops in many environments, not just greenhouse healthy plants do this? Water passively diffuses into
strawberries. Lack of calcium is at the heart of tip roots as nutrient salts concentrate within plant tissues,
burn issues. Plants risk suffering from tip burn when raising internal pressures. During the day, this pressure
grown in environments where calcium supply is is relieved as water transpires through stomata in
low, transpiration activity is low, or light levels are foliage, but at night, stomata are typically closed. Root
exceedingly high. Calcium is a key component of plant pressure is at its highest when soil moisture is high or
cell walls and chemical signaling; without calcium, new transpiration is low. High root pressure during nighttime
cells are unable to properly develop. Damage occurs hours is especially important for the very newest
first on developing tissues such as leaves or calyxes developing plant tissues, which rely on this process for
when sufficient calcium is not able to be translocated. sufficient calcium supply. Guttation is a way for plants
Tip burn manifests on leaves and flower calyxes with to regulate their internal pressures and move water
most greenhouse strawberries. around the plant, which also helps move water soluble
nutrients like calcium to delicate new growth.
The availability of calcium in the root zone is often not
the issue in most cases of tip burn. Since calcium Research originally performed at the University of
transport is driven by water movement through the Arizona by Dr. Chieri Kubota demonstrated that
plant, anything that affects transpiration will affect strawberry plant and fruit quality in the greenhouse
calcium movement. Plants grown under high humidity were greatly increased by control of nighttime vapor
environments are unable to transpire as effectively; tip pressure deficit (VPD). In the greenhouse, growers
burn is a common sight in these situations. High light can have very finely tuned control of environmental
conditions provide another opportunity for plants to conditions, including VPD. Growers should monitor
suffer from tip burn. Especially in the case of lettuce, their relative humidity levels at night and aim for at least
high light can drive fast vegetative growth which can three hours per night of >95% humidity. Growers may
outpace calcium’s ability to move or even stress plants either fog under benches or spray down greenhouse
into closing stomata. floors after sunset to achieve these humidity levels.
Growers will know their nighttime treatments are
So, how can growers know their plants are not at risk working when guttation is observed on strawberry
for tip burn before it happens? Strawberry plants give leaves the following morning.
growers one very helpful signal: guttation. Guttation
is defined as the exudation of xylem sap through Though humidity control is not the only strategy
hydathodes (small pores) at leaf tips and edges. These to combat tip burn, it is the best. In other crops,
exudates often contain plant sugars and nutrients such growers may apply calcium sprays to foliage to deliver
as potassium ions and can leave small white deposits calcium directly to affected tissues. This method is
on the leaves once evaporated. Many different species not recommended for strawberries, which can be
of plants exhibit guttation but can most often be seen susceptible to fungal infections with increased foliar
in ground-hugging plants, low lying foliage, or house moisture. High salt damage can also result in tip burn,
plants. This phenomenon is caused by root pressure though this is not related to calcium supply. Growers
when transpiration is limited and is most often observed should always be aware of salt levels in both their
early in the morning before rising temperatures have irrigation water as well as their growing media.
burned off dew deposits.

GRIFFIN GAZETTE 2022 | 9