Category Archives: Disease

Tan Spot In Triticale

 

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Here is a field of triticale with a pathogen I have not seen before. I noticed these diamond-shaped lesions with a yellow border and dark brown spot in the center of lower leaves. It is called Tan Spot (Yellow leaf spot or Blotch) and is caused by Pyrenophora (Syn. Drechslera) spp. Disease development is favored by frequent rains and cool, cloudy, humid weather. I also noticed some of the leaf tips dying – this is also a symptom.

Lesions may coalesce, causing tip of leaf to die

Lesions may coalesce, causing tip of leaf to die

UGA Extension Pathologist Dr. Alfredo Martinez has this information:

The disease is more problematic susceptible varieties, poor fertility and in fields with wheat residue left on soil surface. Initial infections come from diseased crop debris in the soil, or from diseased grass hosts. Usually the lower leaves are infected first, and the disease progresses to the upper leaves and leaf sheaths if conditions are favorable. This disease develops over a wide range of temperatures and is favored by long periods of dew or rain. Crop rotation with non-host crops reduces the severity of tan spot. Seed treatment seems to be effective in reducing the disease.

Fungicides applied timely are effective in reducing the disease severity and improving yield.  Most fungicides are label to be applied up to Feekes 10.5 (fully headed) but before flowering. Only a couple of triazol fungicides are labeled to be applied for Fusarium Head Blight at 10.5.1, which is flowering.

Tan Spot can be serious by itself or it can contribute to other leaf spot complexes, like Stagnospora Glume Blotch, which we saw last year. This field has already been treated with a fungicide, and the pathogen is not highly infected our flag leaf. This is the leaf below the head which is pulling most of the photosynthate to the grain. This is what we are aiming to protect.

 

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Pecan Budbreak: When To Spray?

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With Friday’s heavy rain and the arrival of budbreak, pecan growers are anxious to get their first fungicide spray on for scab protection. Infection has historically been bad in our area, and growers like to get started early. Here are some points from UGA Extension Horticulturalist Dr. Lenny Wells:

At this point, the only pecan variety growers should be concerned about is ‘Desirable’. Most varieties that have budded out far to this point are less susceptible to scab and is less of an urgency to get those covered. If ‘Desirable’ is to the point where the leaves are unfolding, and you are located in a scab prone area (below 300′ elevation or surrounded by woods), it may not be a bad idea to spray this week. If the leaves are still tightly enclosed in the form of a swollen bud or you are in an area with good air flow, I would hold off at this point.

For most other varieties, especially Stuart – which is further behind in its progression of bud break – there is no need to spray just yet. While we had significant rain Friday and there is a chance of rain one night this week, low temperatures are forecast to remain in the mid to low 40’s, especially toward the end of the week. The optimum temperature range for scab infection is 59-77 degrees F and a leaf wetness of about 12 hours. If the cooler weather this and last week slows down budbreak, it will likely slow down scab as well. Except for ‘Desirable’ in the situation described above, I would plan on waiting until next week to begin scab sprays in most areas of the state.

For an example of a proven fungicide program to consider see a previous blog post on: Example of Fungicide Program to Manage Scab.

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Mayhaws Blooming

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MayhawsBlooming 006Mayhaws are blooming in the county right now. For years, they have been used in the Deep South for cooking. Many folks around make jelly from Mayhaws. Last year, their prices went up and folks were interested in finding trees. Though mayhaws grow well in low areas, like river bottoms, they are also adapted to commercial production and grow good on upland sites with irrigation.

One of the biggest pest issues we have with mayhaws is a disease called Quince-Cedar Rust. Spores infect the tree at bloom each year and then overwinters on a secondary host of a cedar tree – usually Eastern Red Cedar – after this. Infection takes place one time during the growing season. The first thing to do is remove cedar trees within a quarter of a mile of any mayhaws. If many cedar trees are present, this is not practical. In this case, managing rust with a fungicide program is the best option.

UGA Extension Pathologist, Dr. Elizabeth Little, says that myclobutanil is labeled for this disease and can be applied starting at bloom if this disease has been a problem. Be aware that resistance is common with myclobutanil so the further apart your sprays the better. Spray with myclobutanil no more than two times in the growing season. Another fungicide may need to be used following these treatments. Below is a picture of Cedar-Quince Rust.

Quince-Cedar Rust

Quince-Cedar Rust

UGA and UF conducted experiments on mayhaws years ago. Here is a good read for more information: Experiments and Observations on Growing Mayhaws as a Crop in South Georgia and North Florida

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Peanut Nematode Control Update

With more than a month from planting, UGA Extension Pathologist Dr. Bob Kemerait has some information on nematode thresholds and how we decide to use nematicide and/or resistant variety:

Growers who anticipate a problem with peanut root-knot nematodes and who plan to applpy a nematicide will likely use Telone II or Velum Total. The primary consideration in choosing between a resistant variety, Telone II and Velum Total is the size of the population of nematodes in a field. The economic threshold, that “magic” number that draws the line between when damage from the nematodes is worth treating and when it is not, is 10/100cc soil. 

Velum Total (18 fl oz/A) is generally recommended where a grower would have used Temik 15G, 10 lb/A at-plant – which would coincide with “low-to-moderate” nematode populations. Defining “low-to-moderate” populations is unsettling, but I would say anywhere from 10-100 root-knot nematodes per 100cc soil in a FALL-collected sample would be “in the ballpark.”   As numbers increase beyond 100/100cc soil, I think a resistant variety or Telone II becomes increasingly important. 

Also, given that the root-knot nematodes are generally “clumped” in a field, it is likely that even a field described as “low-to-moderate” will have significant “hot spots” in it. Telone II should be applied in-row at 4.5 gal/A in-row 10-14 days ahead of planting with special awareness of soil conditions during this El Niño season. The possibility of frequent rain events could make fumigation challenging.

An insecticide for management of thrips is still required when Telone is used but not when Velum Total is applied. Velum Total should be applied at 18 fl oz/A for peanuts, and the product can be mixed with other fungicides and inoculants without concern. Whether choosing Telone II or Velum Total, accurate calibration and precise application are critical for maximum success. Growers should ensure that equipment is properly put together and tested for calibration.

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Brown Patch Issues In Turf

We’ve been looking at lawn problems with commercial landscape folks this past week, and I thought I’d put a little piece about what we’re seeing. Brown patch (Rhizoctonia solani) is the most common disease I find, and most common disease the diagnostic lab in Athens sees as well. Down here, we see it in centipede, and also St. Augustine. Brown patch is generally a disease of spring and fall. However, temperatures from October through January have been ideal for this pathogen.

Just after Christmas, I was asked to look at lots of centipede yards from homeowners where symptoms looked like brown patch. On the microscope, I never was able to confirm the pathogen. UGA Extension Pathologist Dr. Elizabeth Little confirmed that too much rain – environmental conditions – was to blame for these problems across the state. Once January freezes began, I had no more calls about lawn issues. Grass finally went dormant where lawns were open. We still have green turf under trees – mostly St. Augustine.

Last week, we looked at some St. Augustine affected with brown patch. Much of it is not dormant. It had been treated three weeks ago. Before this, it was treated in November. This inquired lots of questions like is it active? Should we spray again now?

Upon looking at the yard, the symptoms represented old disease. The disease infected during the warm period sometime between December and January. The recent cold weather is too cold for the pathogen to be active.

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Should we treat now?

There are some spots that appear to show some activity. Conditions that favor brown patch pathogen night temperature above 60 degrees and daytime temperature above 80 degrees. Our days have become warmer, though nights are still cool. A pathogen in infected grass could become active during these temperatures. However, does a small chance at pathogen activity warrant a spray? According to UGA Extension Turf Pathologist Dr. Alfredo Martinez, we need consistent days of 65 degree soil temperatures for the right conditions for Brown Patch to exist. Any fungicide sprays now will likely not be effective.

Fungicide treatments in dormant turf?

When turf is dormant, it is not recommended to apply fungicides. Strobilurins (Heritage) and DMI’s (propiconazole) are systemic in the plant. When turf is dormant, these fungicides – which are our heavy hitters for soil pathogens – are not effective. On the other hand, contact fungicides, like chlorothanonil, may be effective on a pathogen in dormant grass. However, with cold temperatures, the pathogen is less or completely inactive.

Keep in mind that managing disease is more cultural than chemical. With brown patch, we need to limit our nitrogen when disease is active. We may also increase our potash. Fertilizers with K only can be used at the end of the season to increase vigor through winter. We also need to watch irrigation. The most common cultural issue I find is lawns watered 2 and 3 times a week. This makes disease almost certain. We need to irrigate between 9pm and 9am and apply enough to give the turf 1 inch of water per week, once per week. Deep, infrequent water events help increase rooting depth and lessen disease conditions. To see more on brown patch, visit Turf Diseases In Georgia: Identification & Control.

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Small Grain Issues

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We spent lots of time this past week looking at grazing and small grain crops. This photo of triticale above is real common in many fields. Stripes indicate nitrogen deficiency between former layby rows. This time last year, we were also seeing affects of barley yellow dwarf virus (BYDV) which is vectored by aphids. Last season, aphids were very bad early (November and December). The earlier planting of small grain/forage crops is more likely to contract BYDV based on early aphid presence. The issue is that we must plant our grazing earlier so they are established.

The presence of aphids were low early this season – opposite of last year. Following Christmas, however, I noticed evidence of aphid feeding was showing up in all small grains. We are now seeing symptoms of BYDV in some fields. The difference in cold injury, BYDV, phosphorus, and nitrogen and potash deficiency can be difficult to tell. Additionally, all elements depend on all other elements – if one is deficient, the whole thing collapses. UGA Extension Forage Agronomist Dr. Dennis Hancock sums up some of the issues we are seeing in the field:

Discoloration can mean different things in different situations. Yellow tips and leaf margins usually mean K deficiency, if N is sufficient. Yellow to tan tips but not leaf margins usually mean cold injury. Purpling tips usually means cold injury, but if temps have been mostly mild and we are dealing with susceptible species (oats, wheat, etc.), then it could also mean BYDV – especially if yellowing extends all the way to the base. Purpling at the base of the plant can also be cold temperature related or it could mean P deficiency. Usually in those situations, it is actually P deficient because of the cold (which slows down mycorrhizal fungi that assist the plant in absorbing P and Zn).

Lower leaves of triticale showing tip burn

Lower leaves of triticale showing tip burn

Symptoms of BYDV on oats

Classic symptoms of BYDV on oats

Fields have been wet the past 2 weeks, and anaerobic conditions could also be causing problems. Growers have been sidedressing when fields have been dry enough. Looking over the past month, some fields are looking better.

 

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Fall Broccoli Close To Harvest

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We have a few vegetables planted  in the county this fall. Here is Brandon Barnes with some bare ground broccoli that was transplanted back in October. This variety is Emerald Crown which is a mid-season variety in Georgia and North Carolina. The heads are coming on now, and some will probably be ready to pick in a week to ten days. The overall plants and color look good across the field. He has a pivot in this field, and we want to make sure we’re putting on an inch more or less of water each week.

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Caterpillars are a common insect pest of cole crops. We have been checking for diamond back moths which is part of the cabbageworm complex. Populations are low in the field right now which is good since management is a challenge with resistance. When scouting, we note the ‘window pane’ effect that is common from diamondback moth feeding.

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Some disease is showing up but not causing real problems. Alternaria is usually observed with concentric ring on a leaf. Another pathogen we may check for is black rot, which is a bacteria in the Xanthamonus genera. Below is a photo of black rot in red cabbage. With black rot you generally see yellowing at the leaf margin, and you will see ‘black veins’ running through the yellow/necrotic area through the light. Lesions are usually characteristic of V-shape. Upcoming cool nights will hold back the bacterium.  So far, a good fungicide program has proved to be effective.

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Black Rot of red cabbage

 

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Crown Rust In Oats?

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I was asked about rust in some oats east in the county. These oats are coming along, getting closer to graze. It has been a little dry here, and many aphids are present. Tip burn is showing up where temperatures dropped. Once we started looking through the field, it was apparent spots on the leaves were the result of aphid feeding. We still need to scout for aphids since they vector barley yellow dwarf virus (BYD). Many times, aphids feeding will leave a small, circular red spot. This appears different than rust since the rust postule is raised from the leaf.

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Aphid feeding

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Aphids

Crown Rust

Crown rust is something we see more in our area south. Like rust we see in wheat and corn, the spores are carried by wind and move long distances easily. The spores overwinter in warmer southern climes and come back to our region in the summer. Rust is identified on the leaf by the small pustules which contain orange-yellow spores. Though grazing and grain are managed differently, UGA Extension Forage Scientist Dr. Dennis Hancock says rust can reduce yields in grazing. If rust is present, it is recommended to grave heavily to reduce the amount of fungal inoculant on the oat crop. We would also have to monitor this close grazing.

The key to differentiating rust from leaf spot or aphid feeding is the orange powder spores on your finger after rubbing the leaf. Here is a photo of rust from Seminole County Agent Rome Ethredge:

Crown Rust - Photo by Rome Ethredge

Crown Rust – Photo by Rome Ethredge

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Leaf Blight & Leaf Rust In Pasture

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Here is a Tift 85 pasture that has been cut twice so far and is showing symtpoms down on the leaves and lower down the stem. We are seeing both leaf blight (helminthosproium) and leaf rust. These issues we commonly see in late summer when weather is warm, usually between 75 degrees F and 90 degrees F, and with high relative humidity.

Leaf Blight

Bermudagrass leaf spot is caused by a fungus from the genus Helminthosporium, and the disease has been informally called Helminthosporium leaf spot, Helminthosporium leaf blotch, or Leaf Blight. Leaf lesions of helminthosporium are irregularly shaped and brownish green to black in color. We may see it in irregular patches. Leaf spots are more numerous near the collar of the leaf blade.

Leaf Blight

Leaf Blight

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Leaf Rust postules

Leaf Rust

Leaf rust or Puccinia disease has similar impacts as Helminthosporium. We will also see red to orange lesions can on leaf and stem. Look for a raised area or blister which is the rust postules like we see in wheat and corn. Rubbing your finger over the leaf will leave a rusty color.

Management

Management is strictly avoidance. Coastal, Tift 44, and Tift 85 have some level of resistance while Alicia is extremely susceptible. But even less susceptible varieties are infected with leaf spot when potassium is low. Most reported leaf spot cases are directly related to low soil potash. Nutrients are removed from bermuda hay fields in about a 4-1-3 ratio of N, P2O5, and K2O with harvest. We need 75 percent as much potash as nitrogen  applied each season. Split applications of K are better in sandy soils. With helminthosporium, removing the inoculant is also recommended. In addition to tying up nutrients, thatch holds water and reduces air circulation. This is a conducive environment for inoculum. The only practical way to reduce thatch is burning in spring before green-up.

Visit Leafspot Diagnosis and Management in Bermudagrass Forages for more information.

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Late Leafspot

Looking at peanuts in the field and having peanuts checked for maturity, we are seeing more leafspot show up. Some growers have said it literally showed up over night. Most of these peanuts are close to the Florida line. We see late leafspot get on these peanuts many times. Some defoliation has been noted. Here is a picture of late leafspot sporulating on the bottom of the leaf.

Late Leafspot

Here are some comments on late leafspot from UGA Extension Pathologist Dr. Bob Kemerait from the 2015 Peanut Update:

  • Finding some leaf spot in a field at the end of the season is usually not a problem. As long as the diseases are controlled throughout the season, limited defoliation (up to about 30 – 40%) is not likely to affect your yeield. The appearance of leaf spot at the end of the season typically does not mean that your program was ineffective or a failure.
  • Some grower in Florida are mixing chlorothalonil with Topson-M or Topsin 4.5F or copper fungicides such as Kocide for their final leaf spot sprays to increase peg strength prior to harvest. What do we recommend in Georgia?
    • Combinations of chlorothalonil and Topsin-M currently provide excellent control of leaf spot.
    • Combinations of chlorothalonil and copper are also effective in the control of leaf spot.
    • Data collected at Clemson University demonstrates that peg strength is not increased with use of Topsin-M, Topsin 4.5F, or copper.
  • Failures in leaf spot management in a peanut field are often linked to:
    • Unacceptable delays in starting your program.
    • Improper calibration of equipment (not enough material applied).
    • Unacceptable delays between applications (weather conditions keep growers out of a field).
    • Rain events immediately after a fungicide application have washed fungicide away.

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