Environ. Horticulture, Pears, Cherries, and Viticulture
University of California
Environ. Horticulture, Pears, Cherries, and Viticulture

Use of Soil Applied Fungicides for Reduction of Charcoal Rot caused by Macrophomina in Strawberry

Introduction: The difficulty of controlling Macrophomina, the causal agent in charcoal rot in strawberry, in California has brought about a renewed interest in non-conventional methods for its management.

The following study is an attempt to investigate two soil applied fungicides and their effectiveness in mitigating loss from Macrophomina infection.

Materials and Methods: The trial was done as a randomized complete block design of four replicates of one bed 35 foot long by 4 foot wide per treatment on Monterey variety strawberries in a field known to be infested with Macrophomina in Salinas, California. See the picture below for a demonstration of the disease severity of the disease on one side of the field; the side on which the study was done was unfortunately (for the study, not the grower) not nearly as severe.

Application: Applications of both fungicides were done 3 times in the early part of the year, March 2, April 12 and May 3, 2017. The fungicide Rhyme (which is labeled for soil application for management of charcoal rot), applied at 7 oz/acre and Merivon, applied at 11 oz/acre, were applied in approximately 40 gallons of water per treatment pumped in with a gasoline powered pump hooked up to the double rows of high flow drip tape. Injection consisted priming the irrigation tape, injecting the material and then flushing the lines.

It is important to note that the use pattern deployed here for Merivon is as of this time NOT a labeled application.

Evaluation:

Plant diameters were taken in the early part of the season to gauge any initial differences in plant vigor.   One measurement across the widest part of ten plants was taken in each treatment replicate and reported in cm.

Yield of strawberry fruit was the principle measure of plant performance in this trial. Fruit picking commenced in May with weekly picks, and then continued from June through early September with twice weekly picks. Only marketable fruit was included, and it was weighed and counted from each plot.

Since the work here involved two fungicides, one evaluation of powdery mildew was also done on May 9, 2017 but the amount of mildew was insufficient for a significant evaluation.

Results were tested statistically on ARM version 9 using a multiple comparison procedure (Least Significant Difference at the 95 percent level of significance) to determine whether the means of counts and percentages per treatment were significantly higher or lower from the other treatments.

Results and Discussion:

Results are given in Tables 1 and 2 below. While disease was evident with weakening plants from the beginning of May on, it was not as severe as the outbreak on the other side of the field and no plants were lost in any of the treatments.

Table 1: Plant Diameters on Two Dates (in cm) of Strawberry in Plots of Soil Applied Fungicides Rhyme and Merivon Compared to an Untreated Check1

Treatment

Apr 12

May 3

Untreated

32.2 a

33.1 a

Rhyme

32.7 a

34.7 a

Merivon

32.7 a

35.7 a

 

Table 2: Fruit Yield and Size (in g) of Strawberry in Plots of Soil Applied Fungicides Rhyme and Merivon Compared to an Untreated Check1

Treatment

May totl

May size

June totl

June size

July totl

July size

Untreated

2214a

35.6 a

4408a

28.4 a

5636a

21.0 a

Rhyme

2169a

35.3 a

4720a

28.1 a

5525a

21.9 a

Merivon

2216a

34.6 a

4454a

27.9 a

6064a

22.1 a

 

Treatment

Aug totl

Aug size

Sept total

Sept size

Season total

Size avg

Untreated

3051a

21.2b

849.0a

20.9 b

16157a

24.1 a

Rhyme

2617a

22.2a

784.5a

21.5 ab

15816a

24.8 a

Merivon

2752a

21.9a

1009a

22.3 a

16496a

24.6 a

1Method used to discriminate among means Fisher's least significant difference procedure. Treatments followed by the same letter have no statistically significant differences.

As seen in the tables above, use of the soil applied fungicides in this trial did not result in any significant yield differences between any of the treatments. It is interesting to note however, that average fruit size in the later months of the study, those being August and September, was significantly larger in the treated plots than the untreated.

Many thanks to the grower, BASF and FMC for really great support on getting this trial done.

The use of several pesticides is described in this post.  As always, before using any of these or other pesticides, consult the label and if there are further questions contact your local County Agricultural Commissioner.

Some of the Macrophomina action on the other side of the test field.
Some of the Macrophomina action on the other side of the test field.

Posted on Friday, October 26, 2018 at 11:40 AM

Comments:

1.
Thanks for the hard work, Mark.

Posted by Thom Flewell on October 30, 2018 at 9:50 PM

2.
Thank you Thom! As a grower collaborator yourself, you know how important grower participation is to make these trials go, and that was very much the case here too.  
 
On another note, save Feb 14 as the date for the Annual Strawberry Production Research meeting. I've got a line up of scientists presenting that will absolutely blow your mind, so make sure to be there!

Posted by Mark Bolda on October 31, 2018 at 9:08 AM

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