April 2019 - 23

PLANT HEALTH
Bacillus-based products are classified as FRAC 44 and include Cease,
Stargus and Triathlon BA. These products are not identical, as they have
unique strains and showed a range from some to good control.
ZeroTol is not classified by FRAC and showed none to very good results
in the six trials I located. Similarly, KleenGrow is not classified and in this
case has shown none to excellent control in seven trials.
A bactericide rotation should be based on seven to 14-day intervals
depending on growth rate of the crop and disease pressure. Bacterial
leaf spots are very fast to develop due in part to the very short life cycle
results in a population explosion in a few days. If you are growing an
organic crop, you can use most of the products listed above.
Figure 4. Acidovorax leaf stripe on canna.
CONCLUSIONS
Follow these steps to minimize losses from bacterial leaf spot diseases
on ornamentals.
* Use only healthy cuttings, seedlings or liners.
* Do not overhead irrigate highly susceptible crops if possible,
or irrigate when leaves will dry rapidly.
* Space plants to improve air circulation/drying time as well
as bactericide coverage.
* Discard badly infected plants.
Get a lab diagnosis for diseases you do not easily recognize. Confusion
between fungal and bacterial leaf spots is very easy and common. So
are mixed infections with both types of pathogens. Rotate bactericides
between different FRAC groups to limit possibility of resistance. Bacteria
multiply very rapidly and are very prone to developing resistance to many
products including copper and streptomycin sulfate.
Spray no more often than once a week. Spraying twice a week will be
counter-productive and spraying more = MORE disease.
Follow product labels! The label is still the law.
A.R. Chase is plant pathologist at Chase Agricultural Consulting LLC and can be
reached at archase@chaseresearch.net.
Figure 5. Xanthomonas on Rex begonia.
Although the begonia species responded somewhat differently to the
bactericides, it was clear that none of the products were 100 percent
safe. The most sensitive species appeared to be the wax begonia but
differences between the species were not significant. Overall, the 6-ounce
rate of KleenGrow was somewhat safer than the three coppers but really
none were safe enough for these begonia species to recommend their
use. Disease severity was greatest on the 'Bonfire Orange' and least on
the 'Prelude Scarlet'. The best control across all begonia species in this
trial was seen with the Phyton 27 and Camelot O.
BACTERICIDE TRIALS
Over 20 trials (mainly from Florida, California and Arizona) have
been reported since 2012 on a variety of ornamentals for control of
Pseudomonas or Xanthomonas (Table 2).
The copper products (FRAC M01) were overall effective for both
Pseudomonas and Xanthomonas with a range of none to excellent
control depending on plant and exact product used. Of this group,
Camelot O and Kalmor are OMRI listed.
The plant extracts EcoSwing and Regalia are also OMRI listed and
although tested in fewer trials during the 2012-2018 period, their
results were significant in about 50 percent of the trials.
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GREENHOUSE PRODUCT NEWS 23
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April 2019

Table of Contents for the Digital Edition of April 2019
