Facebook
X (Twitter)
Reddit
Pinterest
Tumblr
Delicious
LinkedIn
StumbleUpon
Posts Tagged: leaf blotch
A Brief Catalogue of Early Season Transplant Disorders
A few things that growers and field people might being seeing this time of year in strawberry plants.
Salt Toxicity: By far the biggest issue so far in 2012 has been salt damage. This issue is well described in the January 6 post, but a photo is included below for the sake of comparision with the other disorders. To re-iterate, most notable characteristic of salt damage is the burnt margins of the leaves, especially on the more developed leaves. Photo 1 below.
Fumigant Toxicity: Fumigation toxicity is another, fortunately not too common, issue that one will see at this time of year. Every case I have been called out to has involved drip fumigation, and this makes sense, since for several reasons drip fumigants take much longer to exit the soil than shanked in materials like methyl bromide. The process of moving out of the soil was delayed even more in the case depicted below in Photo 2 because of application into the cooler temperatures of late October, 2011. It is notable that, in an attempt to mitigate the fumigant remaining in the beds post fumigation, this field was flushed via the drip tape with a large quantity of water and beds slit several days before planting. Nevertheless, these activities still did not suffice, and the field languishes.
In photo 2 (taken the week of January 9) below, one can see the affected plant is struggling to establish itself and is undersized and yellow. This is probably because its root system was compromised by remaining fumigant (doesn't need to be a lot either, it could have just been a trace) at planting and its root system is still struggling to function normally. While this plant will undoubtedly still survive, it is unlikely to reach full yield potential. The die was cast and its fate determined at the point of planting.
Leaf Blotch Disease: Leaf blotch disease of strawberry normally is found all over Central Coast strawberry fields this time of year. However, since it is dependent on splashing water, it is pretty doubtful that there is much of this disease around this year. Nevertheless, since symptoms superficially mimic those of salt damage it is worth a review.
Generally the lesions of leaf blotch disease consist of tan to gray leaf blotches that commonly, but not always, develop along the margin or edge of the leaflets. The leaf blotches are irregular in shape and are very often surrounded by a purple margin. Affected areas can grow to some size and are able to expand and cover from 1/4 to 1/2 of the leaflet surface. To distinguish leaf blotch disease from salt damage one needs to look for the presence of tiny, brown to black, fungal fruiting bodies in the gray to tan blotches. Photo 3 below.
Photo 1: Salt damage- note severity of burning on margins. Courtesy Steven Koike.
Photo 2: Fumigation toxicity. Plant is weak and not growing well.
Photo 3: Leaf blotch on strawberry. While superficially similar to margin burning caused by salt, note purple margin as well as rings of growth within the brown blotch.
Rains Bring on Leaf Blotch Disease of Strawberry
by Steven Koike, UCCE
Leaf blotch disease of strawberry is being detected in some fields in coastal California this winter. Dependent on splashing water, this disease rarely occurs unless overhead sprinklers are used or rains occur. Symptoms generally consist of tan to gray leaf lesions that commonly (though not exclusively) develop along the margin or edge of the leaflets. 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. Brown to black petiole lesions can also occur. In past seasons leaf blotch has been misdiagnosed as spray burn or phytotoxicity from applied chemicals. If uncertain about the nature of such leaf symptoms, submit samples to the UC Cooperative Extension offices in the coastal counties.
Leaf blotch disease is caused by the fungus Gnomonia comari, which also has the name Zythia fragariae. Zythia fragariae survives on strawberry crop residues. The fungus does not appear to be a true soilborne fungus, so it will not likely persist in soil unless strawberry crop debris is present. The Zythia form is especially dependent on splashing water for spore dispersal and infection. This accounts for the typical appearance of leaf blotch during winter and early spring seasons when there are rains. Leaf blotch is usually considered a minor problem and fungicide treatment programs have not been developed nor are they generally recommended. The strawberry plants usually grow out of the problem. Leaf blotch spread and development is dependent on rains and splashing water, so once the winter rains cease, leaf blotch usually becomes a non-issue for growers.
Photo courtesy Steven Koike, UCCE
Photo courtesy Steven Koike, UCCE
Photo courtesy Steven Koike, UCCE
