Archive for September, 2016


Clemson University Continues the Search for Solutions to Armillaria Root Rot

photo by JONATHAN VEIT, Clemson University


MANAGING ARMILLARIA root rot— the disease all orchardists and scientists alike recognize as the single greatest threat to stone fruit or­chard sustainability in the southeast— has gotten a recent shot in the arm for more research.


The devastating fungus commonly known as “oak root rot” causes more than $4 million per state in peach losses every year, and millions more in control costs. What can be done to halt the spread of this in­sidious, underground problem?


Researchers at Clemson University are dedicated to finding out. Though biological and chemical controls are virtually ineffective and hard on the environment, plant pathologist Guido Schnabel has de­vised a manageable solution. Trees are planted in shallow engineered berms with the top parts of roots exposed above ground. Armillaria fungus does not tolerate extreme temperatures, so it is unable to sur­vive above the soil line. This simple, low-cost solution could drastically reduce the number of trees susceptible to the disease.


Scientists have been studying Armillaria root rot for nearly 100 years. Other advances include the release of plum/peach hybrid root­stocks that have a natural tolerance to the fungus. This solution is not ideal, however, due to the fact that these hybrids generally produce a smaller tree and smaller fruit. The only really effective control tech­nique up to this point has been to avoid planting trees on land previ­ously infested with Armillaria. Now, growers can use Dr. Schnabel’s berm technique to aid in the prevention of infection.


Research on grapes showed that mycelium retreats from excavated roots. Dr. Schnabel extended this finding to investigate the effects of planting peach trees higher up initially. “It is not a silver bullet,” he cau­tions, but goes on to say that “the method does buy growers a few more years of production on replant sites.” Planting peach trees in this man­ner does make them more susceptible to drought stress during the first year, meaning that adequate irrigation must be provided to compensate.


The Advanced Plant Technology Program at Clemson University uses a variety of techniques to research plant diseases. Experts in ge­nomics, genetics, computational biology, plant pathology and physiol­ogy, molecular breeding, and more are working together to solve these expensive problems. This research is part of a larger research project by the U.S. Department of Agriculture called RosBREED. The program focuses on developing and applying modern DNA tests and related breeding methods to deliver new cultivars of rosaceous crops in 22 U.S. breeding programs.


Wells Fargo has provided $150,000 to Clemson University through the bank’s National Food and Agribusiness Division. This grant will be used to further the breeding program and find sustainable solu­tions for problems like Armillaria root rot. Stephen Kresovich, Coker Chair of Genetics and director of Clemson’s Institute of Translational Genomics, has this to say about the grant: “The funding provided by Wells Fargo will allow us to apply advanced genetic and computational techniques to build a foundation for solving a critical problem of peach orchard sustainability in the southeastern U.S. This work, if successful, will lead to a more manageable production system with a reduced need for chemical control measures.” This is good news for researchers and, more importantly, peach growers, as the quest to find a cure for this disease continues on.



What Sunshine State Growers Need to Know about the ‘Participant Pathway to Peaches’ Program and How to Enroll


TEXAS CONSUMERS can now experience the pleasure of delicious southeastern peaches from Florida’s harvest. Unlike California, Flor­ida’s subtropical climate creates smaller, yet sweeter and juicier tree-ripened peaches. The demand for these peach varieties are growing, but one pest stands in the way: the Caribbean Fruit Fly. Peaches are the preferred host for this Caribfly, resulting in stricter export pro­tocols for Florida orchards. Consequently, the Florida Department of Agriculture and Consumer Services (FDACS) created a program called “Participant Pathway to Peaches” that allows peach growers to ship their harvest to Texas. It requires a minimum of 40 acres be trapped weekly at $3.50 per acre. In order for your harvest to qualify for certification, you must follow all scheduled protocols required by FDACs. Here’s how it works:

Phase 1: Grower Participation

  • Step 1: Submit your application for certification.
  • Step 2: Remove non-commercial host plants.
  • Step 3: Sign your Peach Protocol agreement in order to have traps in place.
  • Step 4: Begin the protocol’s bait spray program at least 28 days prior to harvest.

Phase 2: Harvester

  • Step 1: Sign a compliance agreement no less than one week before harvest.
  • Step 2: Have your harvest inspected at least one business day before harvest.
  • Step 3: Follow compliance agreement requirements.
  • Step 4: Transport your fruit to the packinghouse using the guidelines set aside.

Phase 3: Packinghouse

  • Step 1: At least 30 days before packing, you or a packinghouse representative must call the protocol office to initiate survey for qualification.
  • Step 2: Sign your compliance agreement.
  • Step 3: Call the protocol office one business day before packing to schedule an inspection.
  • Step 4: Once the fruit has arrived, the Designated Parcel Identification will be verified against the trapping report. Follow all compliance agreement requirements.

Following these steps will result in your fruit becoming certified for shipment to Texas. You’ll be able to make more money by expanding your market and filling the rising demand for Florida peaches.

If you are a grower, harvester, or packinghouse that is interested in participating, please contact the protocol office. Email for information on submit­ting new parcels for monitoring and certification


Peach Irrigation in an El Nino Year

Monitoring Weather Patterns, Soil Moisture in Orchards, and More

Stone Fruit Specialist and Assistant
Professor, University of Florida,
Gainesville, FL

AS WE CONTINUE headlong into the winter season and many of the peach or­chards are resting for a couple of months, what will this year bring? According to the Climate Prediction Center and the International Research Institute for Cli­mate and Society, a strong El Niño was present for the fall months and will peak during the 2015-2016 winter months. Sea surface temperatures at the equator are well above normal (Figure 1), influ­encing weather patterns across the Unit­ed States (U.S.).

In the southeastern U.S., an El Niño year typically brings to Florida cooler and wetter weather. Unfortunately for peach trees, they are not tolerant of flooding. Thus, this dry period before the peak of the El Niño season is a good time to assess your orchard site and make any drainage improvements nec­essary. Additional trenching, drain tile installation, and grading to direct water away from low spots will help to reduce standing water and flooding in orchards.

The increased precipitation that may come with the 2015-2016 winter may contribute to advancing trees out from ecodormancy after trees are defoliated. Recent warm temperatures are not help­ing to slow the advancement (Figure 2), and a few orchards may have trees that are starting to flower and set fruit. Al­though impossible to control precipita­tion, orchards that have begun emerging from dormancy should not be heavily irrigated, depending upon previous rain­fall events. Precipitation amounts for all Florida Automated Weather Network sites can be found at

Although water stress can reduce fruit set and de­lay leaf emergence, significant transpiration (i.e., water movement from roots to the shoots) in the tree will not occur until there is significant leaf area. Soil moisture status will also determine irrigation scheduling in the late winter and early spring.


There are a number of tools to determine soil water status, and while some may be expensive, there are in­expensive and effective options for in-field monitoring. Soil water status will be influenced by the amount of sand, loam and clay in the soil, and much of the peach acreage in Florida is based on sandy soils that drain very well, reducing excessive soil moisture. However, these types of soils need to be irrigated frequently for short periods to most effectively provide water to peach root systems.

There are three main classes of monitoring soil moisture— volumetric, tensiometric, and hand-feel  of these three classes, volu­metric are perhaps the most expensive and require the most knowledge for in­terpretation of the data.

VOLUMETRIC METHODS estimate soil water content by measuring how fast an electromagnetic pulse is affected by water in the soil. These methods in­clude neutron moderation, time domain reflectometry (TDR), frequency domain, amplitude domain reflectometry, phase transmission, and time domain trans­mission (Muñoz-Carpena, 2015). While neutron moderation and TDR are fairly expensive, the other volumetric methods are less expensive and can be used for ir­rigation scheduling. While soil and site specific calibration are required, the ac­curacy on sandy soils is excellent.

TENSIOMETRIC METHODS are less expensive and include such tools as tensiometers, gypsum blocks, heat dis­sipation probes, soil psychrometers, and granular matrix sensors. These have lower resolution and accuracy than volumetric methods, but their low cost is attractive for season long in-field measurements. However, they are not recommended for sandy or coarse soils (Muñoz-Carpena, 2015), in which much of the citrus and stone fruit or­chards are planted in Florida.

Finally, the “HAND-FEEL” METHOD is the most inexpensive, as it is free! Dig­ging up soil from within the root zone and squeezing the soil to determine the amount of water can help to determine how much irrigation to apply. The ability of the soil to form a ball, ability to rib­bon, amount of loose particles, presence of soil/water stains on fingers and soil color are all used to determine the rela­tive water content of the soil (Klocke and Fischbach, 1998; USDA-NRCS, 1998).

Different soil textures have vary­ing amounts of available water capacity (AWC), which is the amount of water that can be extracted from that soil layer by the plant (Table 1). As in­dicated below, our coarse soils on the ridge and in good production areas have fairly low available water capacity, as well as ability to store water near the root zone.

As you begin to think about irrigation for the next production year, consider using irrigation sensors or tools to help schedule irrigation sets. Early results from or­chards in two Central Florida locations indicate that the amount of water cur­rently being applied can be reduced by as much as 50 percent without reducing yield or fruit size. In pecans produced in the southeastern U.S., recent research has shown that a 38 percent reduction in irrigation did not affect tree water stress, yield or quality (Wells, 2015). We look forward to verifying our initial results in 2016, to save water, and help growers become more efficient.

Thank you to the Southwest Florida Water Management District for funding this research.



Klocke, N.L. and P.E. Fischbach. 1998. Estimating Soil Moisture by Appearance and Feel. Publication G84-690-A, Nebraska Cooperative Extension Service, Lincoln, NE.

Muñoz-Carpena, R. 2015. Field Devices for Monitoring Soil Water Content. Publication #BUL343, Electronic Data Information Service, University of Florida Extension, Gainesville, FL.

United States Department of Agriculture – National Resources Conservation Service. 1998. Estimating Soil Moisture by Feel and Appearance. Program Aid Number 1619. nrcs144p2_051845.pdf.

Wells, L. 2015. Irrigation water management for pecans in humid climates. HortScience 50:1070-1074.


How Do the Revisions for WPS Affect Me This Season?

Extension Agent Hillsborough County

IN NOVEMBER OF 2015, the U.S. EPA passed into rule chang­es to the Worker Protection Standard for Agricultural Pesticides (WPS), which was first implemented in 1995. The original pur­pose of WPS was to reduce agricultural workers and handlers’ ex­posure to pesticides and the risk of pesticide-related illness. The new changes are to help further reduce the risk to workers and handlers. Most of the new changes will not become effective till January 2, 2017. There are four provisions that are delayed and will not go into effect until January 2018. What this means for this upcoming peach season is that workers and handlers will still need to be trained as required by law but you will be able to follow the guidelines that you have been following since the changes will not go into effect until January 2, 2017 for most of the new changes.

Those who are certified WPS trainers or restricted pesticide license holders will still be able to train workers and handlers un­der the new revisions. The Florida Department of Agriculture and Consumer Services (FDACS) is advising that even though it is not required for you to be certified again, attending a new “WPS Train the Trainer” class would be a great way to learn all the new regula­tions. The new training materials will help to ensure you know all the new rules so that your operation will be in compliance with all the new procedures in 2017, and then those that follow in 2018.


Warm Weather Woes from December for Orchardists

Lack of Chill Hours Leaves Peach Growers Looking at Crop Management Techniques


FOR MOST PEOPLE, this winter’s warmer weather— cre­ated by the El Niño weather pattern— has been a welcome occurrence. However, for growers with peach trees in their orchards, the year’s unseasonably warm and wet weather is a cause for concern rather than celebration. It comes down to the fact that many trees that blossom and bear fruit, such as peaches, require a certain amount of chill hours in order to have the volume come harvest. Chill hours are necessary for the trees to produce fruit that’s optimal in both quantity and quality. Unfortunately, the southeastern region’s warm weath­er means the area’s peaches have not received enough chill hours as of yet.

According to Jeff Cook, a Univer­sity of Georgia Extension Agent with Taylor and Peach Counties, peach trees in his mid-Georgia region need 700 to 1,000 chill hours. “We basically only received about 150 hours of chill from October to December,” Cook shares, noting how few chill hours peaches have received thus far. He adds that the region’s un­seasonably warm weather might be doing harm above and beyond simply occupying hours usually filled by cold tem­peratures. “Some feel that warm weather negates chill hours,” Cook explains. “If this is indeed true, then the above figure [of 150 hours] might be high.” In essence, the warm weather might actually combat the chill hours already recorded, much like warm weather in February will melt snow that fell in No­vember, December, or January.

For peach country further south—such as southern Geor­gia and Florida— the prognosis isn’t much better. In terms of chill hours, “they require less,” maintains Cook, “but they are still very short on the chill hours that they need.” It’s been unseasonably warm no matter how far south you go, and the need for chill hours is present in every peach variety.

Adding to the problem, warmer temperatures in Feb­ruary and beyond are a real possibility. “The cold January temperatures have helped get us closer to an amount of chill that will produce a quality crop,” Cook observes. But, with El Niño still in effect, January’s chilly temperatures might not be enough. Between early January and mid-February, peaches can accumulate about 1,000 chill hours, but more warm weather will obviously put that possibility of getting enough chill hours in question, especially if warm weather does indeed negate chill hours.

If peach trees don’t get enough chill hours, then they will likely produce a late or reduced crop. According to Cook, more warm weather would most likely create problems. “We have reached 50 percent of required chill on most of our va­rieties, so warm weather would begin to push trees to break dormancy,” Cook explains. “This would cause a long bloom period with weak blooms, poor fruit quality, and delayed leaf out. We could see severe crop loss in high chill varieties.”

While growers can’t control the weather, there are a few techniques they can try, according to Cook. “There are some production practices (mostly pruning) that growers are em­ploying,” he points out. “We are also trying to determine if an application of a fruit thinning compound might help set a high quality crop.”