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Preparing Your Greenhouse for Fall Crops

• Disinfectants
• Algae Maintenance
• Irrigation Systems


Disinfectants for Greenhouses:

Greenhouse sanitation and disinfecting are steps that will make a
difference in your growing season. Begin by thoroughly cleaning the floor
of soil, organic matter and weeds.

Benches should be disinfected and pots, flats and trays should be new or
disinfected. Disinfect benches by mixing one of the below disinfectants in
a sprayer and spraying all surface areas of the bench, flats and pots.
There are several different types of disinfectants that are currently used
in the greenhouse for plant pathogen and algae control. They are
quaternary ammonium compounds (Green-Shield, Physan 20, and Triathlon),
hydrogen dioxide (ZeroTol, Oxidate), chlorine dioxide (Selectrocide) and
chlorine bleach. All these products have different properties. If
possible, disinfectants should be used on a routine basis both as part of
a pre-crop clean-up program and during the cropping cycle.

Many of you use Chlorine bleach. There are more stable products than
bleach to use for disinfecting greenhouse surfaces. However, when used
properly, chlorine is an effective disinfectant and has been used for many
years by growers. A solution of chlorine bleach and water is short-lived
and the half-life (time required for 50 percent reduction in strength) of
a chlorine solution is only two hours. After two hours, only one-half as
much chlorine is present as was present at first. After four hours, only
one-fourth is there, and so on. To ensure the effectiveness of chlorine
solutions, it should be prepared fresh just before each use. The
concentration normally used is one part of household bleach (5.25 percent
sodium hypochlorite) to nine parts of water, giving a final strength of
0.5 percent. Chlorine is corrosive. Repeated use of chlorine solutions may
be harmful to plastics or metals. Objects to be sanitized with chlorine
require 30 minutes of soaking and then should be rinsed with water. Bleach
should be used in a well-ventilated area. It should also be noted that
bleach is phytotoxic to some plants, such as poinsettias.


Managing Algae

Algae growth on walks, water pipes, equipment, greenhouse coverings, on or
under benches and in pots is an ongoing problem for growers. Algae form an
impermeable layer on the media surface that prevents wetting of the media
and can clog irrigation and misting lines, and emitters. It is a food
source for insect pests like shore flies, and causes slippery walkways
that can be a liability risk for students. To avoid algae build up keep
walks sweep clean and free of puddling water. Reduce the flow of water in
your evaporative cooling system with your gate value. You only need enough
water flow to get the pads wet and should not have water splashing off of
system. The recommended disinfectants can be used to spray on floor where
algae is appearing.


Irrigation Systems

Non-recirculating irrigation systems can be cleaned using a new product,
chlorine dioxide (Selectrocide). It is labeled for disinfecting irrigation
lines and greenhouse surfaces. To thoroughly clean irrigation systems, the
company recommends using two consecutive overnight treatments, and then
flushing the system with clear water, making sure to discard the dislodged
debris. Selectrocide can also be used as a continuous ultra-low dose
treatment.