Page 27 - Griffin Gazette Issue 2 - 2020

With such an impressive list of attributes, why are we not seeing more of them being used in commercial
greenhouses? Microbial insecticides are similar to insect growth regulators (IGRs) in that they take
some time to work. Often multiple applications are needed to achieve sufficient infection levels and high
rates of control. Growers naturally prefer products that work faster when they are available. Education
on how to maximize the effectiveness of these products may lead to increased adoption of microbial
insecticides.

Microbial insecticides work differently than most conventional pesticides, so a discussion of application
strategies is needed. All of the listed insecticides except for Grandevo CG and Venerate CG work
by way of infective fungal spores. The best control is achieved by a series of 3 or more sprays at 3
to 7-day intervals, depending on pest pressure. The idea is to maintain a high level of viable spores
for long enough to achieve a high pest infection rate. In general, microbial insecticides need warm,
moist conditions for a period of time after the application to maximize effectiveness. Late afternoon
or evening applications typically allow for a longer period of higher humidity. Maintaining good cultural
conditions in production areas should allow growers to make occasional late day spray applications
without encouraging foliar disease problems. There are a number of foliar fungicides that are compatible
with some or all of the microbial insecticides mentioned in the table (shown on the next page) when
additional protection is desired.
The addition of an azadirachtin-based IGR such as: Aza-Direct, AzaGuard, Azatin O or Molt-X can
also make these microbial insecticides more effective. They slow down the molting process, making it
less likely that the spores will be lost through molting before they have an opportunity to penetrate the
insects. Below is an example of a spray program for pests such as aphids, thrips or whiteflies:

Day 1- Microbial insecticide tank mixed with azadirachtin IGR

Day 4- Microbial insecticide

Day 8- Microbial insecticide tank mixed with azadirachtin IGR
The addition of an approved surfactant is recommended.

Grandevo CG and Venerate are based on bacteria and work by different modes of action than the
products just covered. However, they also benefit from a similar strategy of a series of consecutive
sprays at intervals of 3 to 10 days depending on pest pressure. They would also benefit from the
addition of an azadirachtin IGR. Best success is achieved for all microbial insecticides when applications
are started when pest populations are low.

Continued on next page.

GRIFFIN GAZETTE 2020 | 27