abotezatu, Author at Viticulture & Enology

Essentials of Vineyard Floor Management

14May

By Michael Cook (June 2017)

Vineyard floor management (VFM) is an often overlooked practice that can substantially influence the performance of a vineyard. The major components involved in VFM include controlling weed pressure, conserving soil, and managing soil water.

Weeds compete with vines for nutrients and water in the soil, can harbor pests and disease, and in a young vineyard can cause shading issues and inhibit good spray coverage. Weed control is particularly important during the first few years of vineyard establishment but should generally be carried out for the life of the vineyard. Before planting a vineyard, invasive and perennial weeds should be suppressed to minimize pressure once the vineyard is planted. As previously mentioned, young vines are especially sensitive to weed pressure, this is because they are unestablished and have a minimal root system, thus mining for nutrients and water is limited to a small area in the soil profile. In order to prevent weeds from competing with vines for nutrients and water, growers should maintain a three to four foot weed free strip under the trellis.

Row middle management is another component to weed management. To minimize erosion, alleviate soil compaction, and prevent rut formation in the vineyard row middles, most growing regions in Texas contain some sort of cover crop. For most growers, this simply consists of native grass. Intentional seeding of an annual or perennial cover crop is also common. Annuals are often seeded in the row middle in Fall and can include mustard and cereal crops, annual ryegrass, and nitrogen fixing legumes such as clover and vetch. They are often tilled under mid to late Spring. The seeding of perennial cover crops offers the benefit of providing soil cover over multiple seasons without the need to replant but must be managed more closely. Native mixes of grasses and wildflowers are recommended. Ensuring the row middles are properly maintained will help prevent unwanted weed infestations under the trellis and reduce insect habitat.

Weeds found in the vineyard can be categorized into two taxonomic groups; the dicots (broadleaves) and monocots (i.e. grasses and sedges). There are many differences between the two groups, including how a grower may manage them. This is one reason why proper weed identification is critical as not all weeds are controlled in the same manner.

Weeds can be further defined by their life cycle. Annuals grow and seed out during one season and either germinate in the Spring or Fall. Biennials grow vegetatively for one year and then set seed the following year; thistle is an example of a biennial. Perennials on the other hand are long lived and therefore are often the most challenging weed to control in the vineyard. Not only do perennial weeds reproduce via seed, they can also propagate vegetatively via rhizomes, stolons, bulbs or tubers.

Both cultural and chemical methods of weed management are utilized in the vineyard, often in tandem. Cultural controls include hand weeding, mulching, burning via propane tank, or with a mechanical implement attached to a tractor. Avoiding trunk and root zones when applying cultural control methods is necessary to prevent diseases such as crown gall as well as serious mechanical injury to the vine. Chemical control is popular with many growers because it can be effective, often requires less labor and equipment, applications can be made quickly, and is cost effective. For optimum efficacy, the appropriate herbicide must be safely applied at the right time. Herbicides are categorized into both pre- and post-emergent types. A pre-emergence herbicide works by preventing weed seeds from germinating and is typically used to control annual weeds. Timing is of the utmost importance. Additionally, many products require a rain event for the product to work effectively. There are a handful of pre-emergence herbicides that target specific weeds and are labeled for use in the vineyard. Read the labels carefully as there are often vine age and soil type restrictions. Post-emergence herbicides are applied once weeds are visually present and are either selective or non-selective in nature. Selective herbicides only control very specific weed species and pose little risk to grapevines. Non-selective herbicides, such as glyphosate, will cause damage to any green tissue it encounters, regardless of species. Glyphosate is routinely used in the vineyard to manage weeds, however, since it is non-selective, grapes are sensitive to spray drift. Installation of grow tubes during the season is recommended to protect young vines from accidental spray drift. Spraying under appropriate weather conditions, using a cone style protector on the spray wand, and installing large droplet size nozzles are additional measures that will help reduce the chance of spray drift. Furthermore, post-emergence herbicides are either labeled as contact or systemic. Contact herbicides damage the plant tissue that receives the herbicide and has a fairly rapid effect on weeds. Systemic herbicides are slower acting products but can translocate throughout the plant, including the roots, which helps ensure a permanent kill. Contact herbicides are often used against annual weeds while systemic herbicides work well for controlling difficult perennial species. It should be noted that “tank mixing” a contact and systemic herbicide or applying one shortly after another is not recommended. Applying these two in tandem with the mindset of ensuring high weed suppression rates is erroneous and is a waste of resources. Using the correct product for weed species present in the vineyard at the proper time is a skill every grower should develop. Controlling weeds is not just for aesthetic purposes but can significantly improve vine performance and should be a part of every growers strategic plan.

For assistance in cover cropping, weed identification, product selection, how to calibrate your sprayer, and what kind of equipment may be suitable for your vineyard operation please contact your local Extension Viticulture Specialist. When purchasing herbicide always read the label and be familiar with the active ingredient(s).

Under no circumstances should growers ever apply phenoxy type herbicides, such as 2,4-D or dicamba, in or near a vineyard. Spray drift and vapor drift from these chemicals can have a detrimental effect on the vineyard, even with just a single application. Phenoxy herbicides are common ingredients in many products used to control broadleaf weeds in residential and commercial lawns and landscapes, land under highway jurisdiction, pastures, and farming operations. The Texas A&M AgriLife Extension Service recently published an in-depth article discussing the danger that phenoxy herbicides pose to grapevines. Please contact your local viticulture specialist for a pdf copy or download your copy here.

Hit The Target without Pesticide Applicator Number

14May

By Jacy Lewis (June 2017)

A number of growers have expressed concern regarding an inability to register their vineyards with the Hit The Target due to a lack of a pesticide applicatory license.

It is possible to register as a producer or consultant without an applicators license, this is extremely important as the majority of grape growers do not have or require an applicators license.

In order to register you must send an email to hitthetarget.kel@gmail.com. They will respond to you with a number you can use in lieu of an applicators license. Additionally, KEL has tutorials on how to register with and use the program that can be found at

How to register: https://www.youtube.com/watch?v=4kZtecYBW74&authuser=0

Adding a Crop: https://www.youtube.com/watch?v=yJnJ7MZfgtE&authuser=0

For more information: Hit The Target

Understanding Pest Control Spray Programs

13May

By Fran Pontash (June 2017)

There is no argument that winemakers prefer quality fruit that is free of disease and insect injury. Quality fruit is an indication of healthy vines and good viticulture management. Healthy vines are capable of producing higher yields with relative consistency, and the vines tend to live longer. This potential for higher return on investment has a solid disease and insect management program serving as its backbone.

Quite frequently we are asked, “Do you have a schedule I can follow so I know when and what to spray?” What we have is more than that. The annually published guide, Texas Grape Pest Management Guide describes fungicide and insecticide applications, the growth stage when certain spray applications are most needed, chemical options, modes of action, efficacy, symptom identification, and more. However, it is up to each grower to determine the ultimate timing and choice of chemical(s) with which to spray his/her vines.

Why can’t we offer a one size fits all prescribed schedule? In order to control diseases and pests, a prescribed schedule would demand one to spray so frequently that he rids the site of all flying, crawling, sporulating, and replicating organisms. This type of spray plan deploys excessive and expensive amounts of chemicals, and is a potential environmental debacle, posing a hazard to humans, animals, aquatic life, and neighborly relations. A clearer understanding of what, when, and why to spray can avoid a cycle of over application.

Integrated Pest Management (IPM). “IPM is an effective and environmentally sensitive approach to pest management that relies on a combination of common-sense practices”. Vineyard practices that alter the environment such as opening the canopy to optimize air movement and sun penetration, frequent mowing and managing irrigation help reduce the number of chemical pesticide applications that are necessary. An IPM strategic plan improves chemical efficacy, whether organic or conventional improving fruit and vine health. It hinges on prevention and since some of the diseases that we wrestle with have no cure, prevention literally pays off by saving vines and crops.

Prevention. Prevention relies on obtaining knowledge of our grapevines, their environment, diseases, insects, and the chemicals we use. This begins with selecting suitable plant material. Grape varieties and rootstocks differ in their ability to tolerate certain diseases, weather conditions, and soil character. There is information available on specific rootstock and variety characteristics, so don’t hesitate to consult with your viticulture program specialist.

In addition, consider that some varieties are more susceptible to certain diseases, insects and animals than others. Some examples are Desmia funeralis, the grape leaf-folder that feeds on Lenoir, powdery mildew on Tempranillo, and deer feeding on Blanc Du Bois.

Sanitation. A clean vineyard can prevent outbreaks. An open, trained canopy maximizes air flow and spray penetration. Wood, leaf, and cluster debris removed from the vineyard floor helps to prevent disease by removing insect eggs, larvae and fungal pathogens on dead and dying plant tissue. Frequent mowing prevents weeds from forming mature seed heads. Uncontrolled weed growth competes with vines for nutrients and water, and weeds typically win leaving vines weakened and vulnerable to drought, nutritional disorders, and insect infestation.

Frequency. Spray applications begin during dormancy and continue until senescence. Pesticides have become more efficient and specific in their mode of action; it is important to rotate chemical applications by their mode of action. Pesticides can be overused to the point that the target pathogens or insects develop a resistance to their particular mode of action. Rotating chemicals with different modes of action helps to avoid overusing some of our most effective chemicals.

Maintaining a healthy canopy begins with dormant sprays and sprays continue until senescence. Pesticides use different modes of action that are often target specific. It is important to rotate applications by mode of action. Using chemicals with multiple modes of action helps reduce the ability of target pathogens, insects, and weeds to develop a resistance to the active ingredients of the pesticide. Read all pesticide labels for target pest, appropriate application and resistance management. Don’t hesitate to consult your viticulture program specialist if you have questions.

Note: Fungicide Groups 3, 7, and 11, signifying modes of action, are repeated and circled in red.

Always read and follow the directions on the label, and calibrate the output of your sprayer to know its rate of application. Use a separate sprayer for herbicides. Some combinations of insecticides, fungicides, and fertilizers can be harmful if tank mixed while others mix easily in a spray application. Before mixing, test the chemical compatibility of what you want to spray. In a jar half filled with water, add the proportionate amounts of each chemical. Shake for 15 minutes. The formation of heat, scum, clumps, and a high degree of solid precipitates indicate chemical incompatibility and should not be applied. Read the following caution found on Rampart’s label:

“COMPATIBILITY Mixing Rampart Fungicide with certain surfactants, foliar fertilizers or other pesticides may cause crop injury. Rampart Fungicide is a slightly acidic buffer solution. Avoid mixing Rampart Fungicide with strongly acidic or alkaline materials. Do not tank mix without first testing the mixture’s compatibility nor apply it without assessing its safety to the crop (phytotoxicity).” (2017. Loveland Products. Rampart Fungicide. p. 3).

Timing. Temperature, rainfall and humidity determine disease and insect emergence, thus they determine the timing and choice of sprays that are most effective. Optimizing the timing increases the efficacy of each application and the cost of each chemical purchase. It requires an understanding of the differences between the diseases, insects, and weeds, their times of emergence, their strengths and weaknesses, and the symptoms and signs that they leave behind. Gaining a better understanding of pests and pesticides is an ongoing process. Good record keeping helps immensely. A custom program can be created from recordings of previous weather conditions, chemicals used, timing, and observations of symptoms. Updating our knowledge base has becomes increasingly important as new technology, urban encroachment, and the discovery of previously unrecognized diseases continue to unfold.

Insecticide applications can be optimized by monitoring the emergence of populations so that the highest number of insects are controlled per spray. Sticky traps for sharpshooters and pheromone traps for grape berry moth help monitor the time and severity of their emergence.

General. Most newly planted vineyards experience a grace period in regards to grape fungal diseases. The diseases eventually infect your vineyard, overwinter in it, and take advantage of tender new growth each spring. Insect pests such as grasshoppers and vectors of Pierce’s Disease prefer tender growth and feed on new tissue especially in areas of high risk to insect pressure.

The Grape Pest Management Guide outlines disease and insect pressure by vine growth stage. The outline includes lists of our most frequently used chemicals. Efficacy and modes of action are also included. Don’t hesitate to contact a program specialist with your specific questions.

Grapevine Cold Hardiness

10May

by Pierre Helwi and Justin Scheiner (April 26, 2018)

Cold hardiness is the ability of dormant grapevine tissues to survive cold temperatures during autumn and winter. It is often expressed as the temperature that causes mortality of 50% of primary buds in midwinter, termed “lethal temperature 50” (LT₅₀).

During dormancy, vines gradually acquire tolerance to cold in response to exposure to low temperatures, to reach a maximum tolerance level that is dependent on the grape variety, the environment and cultural practices (Table 1).

Cold hardiness class	Range of critical temperatures	Species	Example of varieties
Very tender	5 to -5°F	Most Vitis vinifera	Chenin blanc, Merlot, Semillon, Syrah, Sauvignon blanc, Zinfandel
Tender	0 to -8°F	Most Vitis vinifera	Chardonnay, Cabernet-Sauvignon, Gewurztraminer, Pinot gris, Pinot noir, Sangiovese, Viognier
Moderately tender	-5 to -15°F	Some Vitis vinifera and some hybrids	White Riesling, Cabernet franc, Gamay noir, Chambourcin
Moderately hardy	-10 to -15°F	Most hybrids	Chardonel, Traminette, Norton, Vignoles
Hardy	-15 to -20°F	Most Vitis labrusca	Concord, Niagara
Very hardy	-20 to -30°F	Some hybrids	Frontenac, Foch

Table 1. Relative cold hardiness of various grape genotypes. Adapted from Dami (2007), Freezing and Survival Mechanisms of Grapevines. Workshop Proceeding.

The cycle of cold hardiness is U-shaped pattern and contains an acclimation period (transition from cold-tender to cold-hardy state) and a deacclimation period (transition from a cold-hardy to a cold-tender state) with maximum hardiness during winter months (Figure 1).

Figure 1. Cold hardiness in grapevines. Figure from Zabadal et al. (2007).

Factors that influence cold hardiness

Temperature fluctuations during mid-winter: vines gradually acquire tolerance to cold as a result of exposure to cold temperatures. Exposure to warm temperatures for even just a few days can cause deacclimation which is more rapid than the acclimation process. Thus, grapes are more likely to sustain winter injury if cold temperatures are preceded by a period of warm weather.
Rapid temperatures drop: this phenomenon can cause trunk splitting which serve as an entry point for pathogens and can trigger crown gall.
Duration of low temperature period can affect mainly the extent of trunk damage, especially in big old trunks where it may take longer for the core to reach ambient temperatures.
Plant genetics: Vitis vinifera cultivars are generally the most sensitive to cold winter temperature extremes, French hybrids are generally hardier, and native cultivars are often the toughest.
All sources of stress such as diseases, mineral deficiencies, inappropriate water status, virus infections… All sources of stress can reduce grapevine cold hardiness during the winter.
Vines out of balance: over-cropped or under-cropped vines are more susceptible to cold damage than balanced and healthy vines.
Limited canopy management and sunlight exposure: practices and training systems that enhance photosynthesis also enhance wood maturation and tissue cold hardiness. A poor managed canopy that increase shading and limit sunlight exposure increase vine susceptibility to injuries due to unripe wood.
Site mesoclimate and site topography: vines in frost pockets that accumulate cold air are more prone to cold injuries.

Cold damage on buds and trunks

A grapevine bud is a compound bud consisting of three growing buds: a primary bud that will emerge first and gives the largest clusters, and a secondary and tertiary buds which are smaller and less fruitful. Cold injury in response to low temperatures typically affects the primary bud first. If the primary bud is killed, the other two buds, which are often hardier, may have survived and will take over instead. Bud injuries can be evaluated after cold damage. Guidelines for determining bud injury can be found online from Cornell University.

Cold damage to trunk can cause splitting which forms an excellent gateway for diseases such Crown gal caused by Agrobacterium vitis (Figure 2B). Trunk damage will manifest itself in spring by generating excessive sucker growth (Figure 2A). Vineyards heavily affected by cold can die immediately or weaken and die 2-4 years later.

Figure 2. Syrah vine damaged by winter low temperatures in West Texas.

Strategies to mitigate cold damage

Wisely match variety with site in order to minimize or eliminate losses to winter damage: cold-sensitive cultivars should be planted only on sites that ensure good cold air drainage.
Prune cold-hardy cultivars first and finish with the least hardy in order to adjust pruning level: for bud adjustment and according to Zabadal et al. (2007), if less than 15% bud injuries occurred, no need for adjustment. If bud mortality is between 15-35%, retain 35% more buds, if between 35-50%, retain 100% more buds. If bud mortality is more than 50% it may not be cost effective to do any dormant pruning or at least very minimal pruning.
Good vineyard management that maximizes vine cold hardiness (adequate irrigation and fertilization, optimal crop load, good disease and weed management…).
Vines with multiple trunks: if one of the trunks collapse, there may still be another trunk that produces a crop and provides some income until new trunks can be established to replace the damaged one (Figure 3).
In sites where trunk injury is expected, hilling-up soil over graft unions can protect scion buds for re-establishing trunks following a cold event that damages buds. Another suggestion is to have the graft union as close to the ground as possible where it is warmer.
Wind machines can be used during temperature inversions to mix warmer above-ground air with cold air, thus raising temperatures above bud-injuring levels at the trellis.

Figure 3. Syrah vine with two trunks, one damaged by cold temperatures and one growing normally.

Recovering after cold damage

After winter injury, a collapsed vine with healthy roots will throw new shoots that will emerge at the base of the plant. Shoots will also often emerge higher on the vine from the most sunlight-exposed nodes on the trellis, or from the basal buds at the base of canes. Many of the shoots will emerge later than normal because they develop from secondary, tertiary or basal buds.

On an own-rooted vine, shoots that emerge at the base, known as suckers, can be used to make new trunks and restore the plant to productive status. However, this cannot be done if renewal shoots are emerging from below the graft union of a grafted vine. In this case, growers may have to start over with new vines, unless a bud just above the union remains viable and emerges.

It is recommended to retain several suckers (3 or 4 suckers) because some may be damaged during the season or eventually develop into large, vigorous bull canes. Moreover, more suckers equal more leaf area essential for recovery and for root system. It is also recommended to not to add any nitrogen fertilizer as this will largely increase the growth of remaining shoots. After training the new trunk, extra suckers can be pruned next season.

As mentioned earlier, damage trunks are prone to Crown gal. If Crown gall develops, galled trunks can be nursed through the season to produce at least a partial crop while suckers from below the galls are trained up as renewal trunks. Old trunk and fruiting canes can only be pruned when the total complement of buds needed for the vine can be obtained on new trunks.

In addition, on severely winter-injured vines, delaying or eliminating pruning is recommended. It allows the adjustment of bud numbers later in the season, reduces vigor of remaining canes and provides greater leaf areas for vine recovery.

Replant decision

Following winter injury, growers have the option of replanting missing vines, or abandoning part or all the vineyard. Replanting vines is costly but replanting also offers the opportunity to make strategic changes to improve overall vineyard profitability and viability.

Factors to consider when deciding to replant after winter injury: site mesoclimate, frequency of cold injury, soil characteristics of the site, performance of variety/rootstock combination, vineyard design and profitability and history of yield and fruit quality.

Cold hardiness is largely dependent on vine environment, health and genetics and it may be an important consideration when selecting varieties for the High Plains and West Texas.

For further reading:

Dami (2007), Freezing and Survival Mechanisms of Grapevines. Workshop Proceeding.

Kamas, Identifying and Managing Winter Injury, Texas Winegrower Volume II, Issue 1

Strik et al. Winter Cold Injury; Oregon Viticulture.

Zabadal et al. (2007). Winter Injury to Grapevines and Methods of Protection. Michigan State University, Extension Bulletin E2930.