Posts Tagged: powdery mildew

April Gardening Tips: Powdery Mildew

As you practice social distancing during COVID-19, you may find yourself spending more time in the...

Keep an Eye out for Powdery Mildew

This time of year, you may notice a white, powdery looking growth on fruit, vegetable plants or...

Fungicide Trials for Fruit and Foliar Pathogens of Strawberry 2013-2014

Summary: In 2014, the authors evaluated fungicide products against a slate of several registered fungicides and an untreated control. Fungicides were tested for efficacy against gray mold caused by Botrytis cinerea and powdery mildew caused by Podosphaera aphanis.

Introduction: The authors have been engaged in studying fruit and foliar pathogens in strawberry since 2007. While this group of pathogens includes anthracnose caused by species of Colletotrichum, leather rot caused by Phytophthora cactorum and angular leaf spot caused by Xanthomonas fragariae, the fungicide screening of 2014 concentrated on the two most common problems: gray mold caused by Botrytis cinerea, and powdery mildew caused by Podosphaera aphanis. Year after year these diseases are the most important foliar/fruit concerns for growers, and subsequently garner the most attention from fungicide distributors and manufacturers.

 

Materials and Methods:

Powdery Mildew: The trial consisted of treatments (Table 1) arranged in a randomized complete block design with each treatment replicated four times, on the Holly Ranch managed by Dole on the variety Monterey. Applications of all materials were made in the equivalent of 150 gallons per acre with a motorized backpack sprayer and hand held boom configured with ten 8001 flat fan nozzles operating at 120 psi, which is intended to closely mimic the conditions of commercial application. Applications of all materials were made two weeks apart: May 16, May 28, June 16, and June 24, 2014.

Powdery mildew evaluations were done on June 5, June 19 and July 7 and consisted of taking ten strawberry leaflets (per plot) of young to mid-age and assigning a percentage on a scale of 0-100% (in 10% increments) to the level of powdery mildew severity on the underside.

 

Table 1: 2014 Powdery Mildew Treatments

 

	Test Material	Rate/acre
	Thiram   24/7	2.6   qt
	Thiram   24/7 2.6 qt+ Procure 480 SC	8   fl oz
	Thiram   Granu-Flo	4.4   lb
	Pyriofenone	4   fl oz
	Pyriofenone	5   fl oz
	Pyriofenone 4 fl oz +   Quintec	6 fl oz
	Quintec	6   fl oz
	Rally	5   oz
	Rally   5 oz w/ Quintec	5   fl oz
	Merivon   + Nufilm P	8   fl oz + 0.01% v/v
	Merivon   + Nufilm P	10   fl oz + 0.01% v/v
	Pristine	23   oz
	Torino   3.4 fl oz w/ Mettle	5   fl oz
	Isofetamid	17   fl oz
	Isofetamid + IB8111	10.3 fl oz + 5.57 fl oz
	Isofetamid + 18121	10.3 fl oz + 16.5 fl oz
	Isofetamid + IB18220	10.3 fl oz + 7.6 fl oz
	Untreated   check	-

 

Results for 2014 Trial

 

Table 2: 2014 Powdery Mildew Evaluation- Percent Leaf Disease by Treatment

 

Character   Rated		% Infest		% Infest		% Infest
Rating   Date		Jun-5-2014		Jun-19-2014		Jul-7-2014
Number   of Decimals		2		2		2
Trt	Treatment
	Name	1		2		3
1	Thiram   24/7 2.6 qt	23.44	a	17.25	bcd	23.08	abc
2	Thiram   24/7 2.6 qt+ Procure 480 SC 8 fl oz	11.88	cde	7.25	gh	14.64	def
3	Thiram   Granu-Flo 4.4 lb	16.25	bc	18.00	bc	26.35	a
4	Pyriofenone   4 fl oz	13.44	cde	13.00	def	15.85	cde
5	Pyriofenone   5 fl oz	13.13	cde	8.25	fgh	8.90	fgh
6	Pyriofenone 4 fl oz + Quintec   6 fl oz	15.31	bcd	11.25	efg	13.60	d-g
7	Quintec   6 fl oz	15.00	bcd	15.50	b-e	23.55	ab
8	Rally   5 oz	16.25	bc	19.25	b	29.40	a
9	Rally   5 oz w/ Quintec 5 fl oz	10.31	c-f	14.00	cde	17.26	bcd
10	Merivon   8 fl oz + Nufilm P 0.01%	6.88	ef	4.25	h	6.76	hi
11	Merivon   10 fl oz + Nufilm P 0.01%	3.75	f	3.75	h	3.49	i
12	Pristine   23 oz	21.25	ab	13.00	def	22.66	abc
13	Torino   3.4 fl oz w/ Mettle 5 fl oz	7.19	ef	7.00	gh	8.67	gh
14	Isofetamid   17 fl oz	11.88	cde	8.75	gh	11.47	d-h
15	Isofetamid 10.3 fl oz +   IB8111 5.57 fl oz	10.63	cde	11.75	efg	15.71	cde
16	Isofetamid 10.3 fl oz + 18121   16.5 fl oz	11.94	cde	4.75	h	10.84	e-h
17	Isofetamid 10.3 fl oz +   IB18220 7.6 fl oz	9.06	def	7.25	gh	10.98	d-h
18	Untreated   check	20.94	ab	24.75	a	30.04	a
LSD   (P=0.05)		6.768		4.920		0.838t
Standard   Deviation		4.786		3.479		0.593t
CV		36.12		29.53		14.89

Means followed by same letter do not significantly differ (P=0.05, LSD)

 

Botrytis Gray Mold: The trial consisted of treatments (Table 3) arranged in a randomized complete block design with each treatment replicated four times, on the Holly Ranch managed by Dole on the variety Monterey. Applications of all materials were made in the equivalent of 150 gallons per acre with a motorized backpack sprayer and hand held boom configured with ten 8001 flat fan nozzles operating at 120 psi, which is intended to closely mimic the conditions of commercial application. Applications of all materials were made two weeks apart May 16, May 28, June 16, and June 24, 2014.

 

Evaluations for Botrytis infected fruit were made during the weekly fruit harvest by a professional crew of research plot harvesters beginning May 21 and continuing until July 16. Culls were sorted and examined for symptoms and signs of gray mold disease, and a percentage of gray mold infected fruit was calculated from the total fruit harvested from that plot.  Data results (Table 4) is presented as a percentage of Botrytis infected fruit from the  total amount harvested.

 

Table 3: Test materials for Botrytis study

 

	Test Material	Rate/acre
	Thiram   24/7	2.6   qt
	Thiram   24/7 2.6 qt+ Procure 480 SC	8   fl oz
	Thiram   Granu-Flo	4.4   lb
	Merivon   + Nufilm P	8   fl oz + 0.01% v/v
	Merivon   + Nufilm P	10   fl oz + 0.01% v/v
	Pristine	23   oz
	Isofetamid	17   fl oz
	Isofetamid + IB8111	10.3 fl oz + 5.57 fl oz
	Isofetamid + 18121	10.3 fl oz + 16.5 fl oz
	Isofetamid + IB18220	10.3 fl oz + 7.6 fl oz
	Untreated   check	-

 

Table 4: Results for 2014 trial

 

Character   Rated		% Bot		% Bot		% Bot		%Bot		%Bot
Rating   Date		Jun-4-2014		Jun-11-2014		Jun-18-2014		Jun-25-2014		Jul-3-2014
	Treatment   Name	3		4		5		6		7
1	Thiram   24/7 2.6 qt	4.21	a	1.68	a	3.15	ab	8.75	a	18.01	a
2	Thiram   Granuflo 4.4 lbs	7.22	a	1.07	a	1.95	abc	15.17	a	18.39	a
3	Thiram   24/7 + Procure 480 SC	9.27	a	2.49	a	1.64	abc	14.36	a	16.198	a
4	Merivon   @ 8 fl oz	5.52	a	1.49	a	0.74	c	15.56	a	16.268	a
5	Merivon   @ 10 fl oz	5.96	a	1.25	a	0.69	c	15.73	a	17.233	a
6	Pristine   @ 23 oz	7.46	a	1.44	a	3.49	a	12.32	a	14.708	a
7	Isofetamid   @ 17 fl oz	6.54	a	1.07	a	1.67	abc	12.70	a	17.975	a
8	Isofetamid @ 10.3 fl oz +   IB8111 @ 5.57 fl oz	5.67	a	1.58	a	1.35	bc	10.86	a	20.643	a
9	Isofetamid @ 10.3 fl oz + IB18121 @ 16.5 fl oz	4.69	a	2.11	a	2.63	ab	8.60	a	12.815	a
10	Isofetamid @ 10.3 fl oz +   IB18220 7.6 fl oz	5.59	a	1.85	a	1.87	abc	9.22	a	19.803	a
11	UTC	13.52	a	1.68	a	3.14	ab	7.66	a	14.720	a
LSD   P=0.05		0.344t		0.276t		0.265t		0.282t		8.9782
Standard   Deviation		0.238t		0.191t		0.183t		0.196t		6.2180
CV		27.11t		46.46t		39.85t		17.79t		36.62

 Means followed by same letter do not significantly differ (P=0.05, LSD)

Discussion of Results for 2014 Trial:

 

Powdery Mildew: Control of powdery mildew by both rates of Merivon and a rotation of Torino and Mettle was exceptional, with percentages of infection significantly lower than many treatments in each of the three evaluation dates.

 

Looking at the last rating date on July 7, neither formulation of Thiram controlled powdery mildew, but the inclusion of Procure together with Thiram 24/7 did result in disease percentages below the untreated control. Test compounds isofetamid and pyriofenone had lower percentages of mildew than the untreated control. Rally 40W did not have significantly lower percentages of mildew than the untreated control.

 

Botrytis: With the exception of the June 18 evaluation date, no significant differences were found between any of treatments. On June 18, both treatments of Merivon demonstrated lower levels of Botrytis infected fruit than the untreated control, Thiram 24/7, isofetamid @10.3 fl oz + IB8111 and Pristine.

 

Final Note: The use of fungicides, including unregistered materials, is the topic of this article. Before using any of these products, check with your local Agricultural Commissioner's Office and consult product labels for current status of product registration, restrictions, and use information.

 

Acknowledgments.

We thank Patty Ayala, Kat Kammeijer and Monise Sheehan for their assistance with this trial. We acknowledge the California Strawberry Commission and cooperating companies, in particular Dole, for supporting this work.

 

Powdery mildew loves your garden, too!

Seeing white powdery growth on leaves and shoots in your garden or landscape? It's probably a sign...

Powdery mildew, Sphaerotheca pannosa, on rose.

Powdery mildew, Sphaerotheca pannosa, on rose.

Protecting food crops from powdery mildew

It looks harmless enough – a light dusting like baby powder sprinkled on the leaves. But powdery mildew can attack new buds and shoots, stunt growth and distort plant development. If not controlled, the fast spreading fungus can cause billions of dollars of crop damage in California. For example, powdery mildew is the most significant disease affecting grapes in California, with all productive acreage treated to help minimize loss. Borne by the wind, its spores race through fields and can easily damage a season's crop, resulting in losses of 30 percent or more.

Growers combat powdery mildew with sulfur, fungicides, and other deterrents, but treatment is costly, and timing is difficult. But a much more precise strategy may be on the way.

Using highly refined dissection of infected plant cells, coupled with genetic analysis, UC Berkeley plant and microbial biology associate professor Mary Wildermuth identified genes critical to a plant's response to mildew attack. Her research focuses on a plant breeding strategies that can weaken powdery mildew's grip.

With the funding from UC Berkeley's Bakar Fellows Program, which supports early-career faculty conducting commercially promising research, Wildermuth is applying her discoveries to protect commercially valuable crops. She uses a plant in the mustard family popular with researchers for it small, sequenced gene and a short life cycle.

“We've already identified the parallel genes in a number of important crops,” she said. “By targeted breeding to limit these genes' powdery mildew-promoting effects, we should be able to protect plants without extensive chemical treatments.”

When powdery mildew spores land on a leaf, the spore germinates and bores through the leaf surface to make a lobe-shaped feeding structure. The fungus also influences nearby plant cells, manipulating the leaf cell physiology to gain nutrients. A high nutrient supply is needed to support the large fungal network on the leaf surface and the formation of new spores, which propagate the infection.

Wildermuth's lab used a highly refined technique under an optical microscope to scrutinize the fungus-plant interaction and focus in on the plant cell housing the fungal feeding structure and the neighboring leaf cells.

"We can see these cells under the microscope and use the laser to cut them out. The dissected cells literally drop into a tube below," she said. "It's quite fun to do."

The research team isolated the cells and extracted the RNA. They then determined which genes are turned on and which are turned off in specific cells at the infection site versus uninfected cells. They zeroed in on genes likely to be critical to the infection process, and used plants in which these genes were knocked out in order to see if the plants respond differently to powdery mildew. 

The lab identified a set of genes that actually help the mildew fungus steal more food from the plant. The process, called endo-reduplication, allows cells in the leaf to increase production of DNA without dividing – one of the few ways cells can increase their metabolism and size, Wildermuth says.

“The fungus induces endo-reduplication in the plant cells underneath the feeding structure, and gains access to more nutrients in the leaf.” This, in turn, spurs fungal growth and reproduction. “We showed that if the DNA-enhancing process is blocked, the fungus gets put on a diet, and its proliferation is limited,” she says. 

The Bakar Fellowship supports her current effort to determine whether similar genes in grapes, tomatoes and other crops threatened by powdery mildew can be targeted to limit the fungus's growth. Crop strains in which these genes are less active or even absent could be selectively bred to thwart fungal growth.

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