Just a quick note and pictures to add to our growing catalogue of physiological damage to strawberries and caneberries.
Depicted below are several instances of sunburn and/or heat damage to strawberry. The top two pictures were of a strawberry plant up next to a wall getting full sun during the entire hot spell we had last week, so it is without a doubt it is heat and sun which caused the damage depicted in the pictures below.
These are good features to recognize for the diagnostician in the field.
- Author: Steven Koike
- Author: Mark Bolda
Leaf blotch disease, caused by Zythia fragariae, is a very minor foliar disease of strawberry in California. Usually the disease occurs in late winter/early spring when there are sufficient rains to activate the fungus and spread the spores. Once the winter season rains have ceased, the disease subsides before the development of much fruit. Because of the drought, leaf blotch was generally not observed or reported during the late winter/early spring of this season.
However, an unusual flare-up of leaf blotch is currently developing in some fields in the central coast. Because of the lack of rainfall and build up of salts in the soil, some growers used sprinklers in the early spring to alleviate salt buildup and reduce subsequent stress of the strawberry transplants. It appears that in some cases, the sprinkler irrigations have enabled Zythia to develop and cause typical leaf blotches. Symptoms consist of tan to gray leaf lesions that commonly (though not exclusively) develop along the margin or edge of the leaflets (Photo 1). Leaf blotches are irregular in shape and may be surrounded by a purple border. These affected areas tend to grow fairly large; they can expand and cover from 1/4 to 1/2 of the leaflet surface. A key diagnostic feature of leaf blotch is the presence of tiny, brown to black, fungal fruiting bodies in the gray blotches (Photos 2 and 3). These fruiting bodies produce tiny spores (Photo 4) that are readily spread by splashing water.
A related development is the formation of brown to tan lesions on the calyx tissue of strawberry fruit (Photo 5). Calyx lesions appear to be associated with plants having the leaf symptoms. In some cases, the Zythia fruiting bodies are present in the calyx lesions and appear as darker brown, circular to oblong structures (Photo 6). However, fruiting bodies are not always present; since there are other physiological or environmental factors that can result in damage to fruit calices, care should be taken when diagnosing this problem.
UC Cooperative Extension does not have efficacy data for fungicide use for leaf blotch; therefore, we do not recommend or suggest the use of fungicides. Researchers in other areas (Europe) have determined that the following materials have good effectiveness against the leaf blotch pathogen: Pristine, Quadris, Rally. Switch also reduced disease but was less effective. This April occurrence of leaf blotch following sprinkler irrigations is a good reminder of how environmental conditions are essential for the development of plant diseases. This leaf blotch situation may continue to be present if any late April rains fall.
There are fungicides mentioned for management of leaf blotch disease in this article. As always, 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.
For grower and PCA reference, this sample came into Steve's lab on Monday. No disease found, and checking with the grower it showed up in the warmest part of the field one day after application of 32 fl oz per acre of Diazinon 2E. Interestingly, it showed up on the fruit only, not on the leaves or flowers. Problem is starting to clear, with new incoming fruit looking fine.
I have had occasion in my travels over the past two weeks to find a good quantity of what is depicted in the two photos below: J-rooting of strawberry plants.
J-rooting of strawberry plants occurs when the root is too long for the planting hole (Photo 1 below shows how big a healthy transplant can be - lots of those this year by the way) which has been made for it and subsequently the root tips end up pointing upwards rather than down. All too frequently, these upward pointing root tips end up being outside of the hole in the open air, as depicted in Photo 2 below.
It is not difficult to understand why J rooting is not beneficial to the plant. Root extension in plants takes place from the root tips, and having them exposed to the open air, drying out and dying does nothing to help this process along and represents a setback to the establishing plant. To be blunt, it’s a bad practice to be planting this way and shows a costly lack of attention to detail.
Transplanting is hard, back breaking work and it’s not too difficult to empathize and understand how J rooting can happen all too easily. Growers can help their planting crews along and get the roots straight down by several ways. Already having a deep hole or slot to be placing the transplant into helps a lot. Additionally, growers can ask that nurseries trim the roots to reduce the length of root of the transplant to better the odds of everything going straight down. In field quality control on the day of planting by the person in charge also goes a long way in making sure J rooting doesn’t become a pattern in for one individual or the crew.
A response to the question posed to us concerning how soon one should be applying water to Chateau (flumioxazin) sprayed in the furrows for weed control in strawberry. The label says that this herbicide can be applied at a minimum of 30 days before transplant of strawberries, but it doesn’t seem to specify how soon to apply the water after application.
Probably the sooner you apply water to furrows the better, but in a study run by Oleg in Ventura County, Chateau was applied to furrows about a month before sprinklers were turned on and the herbicide was effective against several broadleaf weed species, including wind-dispersed weed seed that landed in furrows after application.
Chateau does not degrade and just remains on soil surface, provided furrows stay dry during that time. If the furrows get wetted enough to germinate weeds the herbicide will be sufficiently activated as well.
The residual efficacy of Chateau is diminished over time, but you can reapply it to furrows if needed – there is no co-distillation, so as long as there is no drift, strawberry plants should be safe. You can extend the control by reapplying it with shielded sprayer in-season as long as the strawberry plants do not have flowers and fruit (which is soon in Southern California but quite a bit later here in Watsonville and Salinas) and you do not intentionally overspray the beds (first photo below) .
Also, thinking about traffic going through the field after application, specifically the wheels of tractors moving through the furrows, it does create some breaks in the barrier that the initial application of Chateau has formed. It might be interesting to do a little experiment with different levels of disturbance post-application to see how much efficacy really is affected. However, remember that Chateau can be reapplied later on in December and January in the furrows in order to get better control since it will be catching multiple flushes and cohorts of weeds from both the seed bank and wind dispersal.
UC IPM guidelines for Chateau in strawberry are available at:
The use of flumioxazin (Chateau) is extensively written about in this article. Before this or any other product, check with your local Agricultural Commissioner's Office and consult product labels for current status of product registration, restrictions, and use information.