Ch. 8 Hazards, Pests and Diseases Flashcards
What is the minimum amount of water needed in warm and cool regions to produce quality fruit at viable yields?
500mm in cool climates
750mm in warm climates
What are the effects of drought on the vine?
Through the process of transpiration, open stomata (pores) on the underside of grape leaves diffuse water vapor, while the vine pulls more water from the soil to compensate.
When there is drought and the vine is going through water stress, the stomata will close up to avoid the loss of water. However oxygen and CO2 are also exchanged through stomata. When the stomata close, there is not enough CO2 coming into through the leaves and photosynthesis is slowed down or even stopped.
Photosynthesis is how a plant generates energy to continue growing and ripen grapes, so both of these processes can be stunted if there is drought. This means potentially unripe grapes or lower yields. If drought continues over extended period of time, vines will lose their leaves and die.
What management options exist for drought?
- Irrigation systems should be considered in vineyard design. Can be fitted later but more expensive and disruptive.
- Choose drought-resistant rootstock from V. rupestris or V. Berlandieri parentage (like 140R and 110R)
- Choose drought-tolerant variety (like Garnacha)
What are the effects of too much water on the vine?
An excess of water can have different effects on the vine at different stages of the vine cycle.
- late spring/early summer - excess water will promote vegetative growth into the grape ripening period, and will compete for vine’s energy and resources, compromising ripening
- too much vegetative growth can cause excessive shading of grape bunches, which if not managed by canopy management, can reduce the development of anthocyanins, tannins, aroma compounds and polymerisation of tannins and higher levels of methoxypyrazines
- dense canopies decrease ventilation which encourages fungal disease - later summer/early fall - too much water late in ripening period can cause dilution of sugars, grape splitting (which then encourages botrytis)
If soils are not free draining (i.e.clay), they can become waterlogged, limiting O2 available to roots, slowing down growth and potentially killing vine
Waterlogging makes soils more compact, difficult to work and uncontrolled water run off
How can a grape grower manage the effects of excess water?
- Plan on slope
- Plant on free draining soils
- drainage system
What are the effects of untimely rainfall on the vine?
Untimely rainfall can affect the vine in different stages of the vine life cycle.
- During pollination and fruit set - can cause millerandage (high proportion of seedless grapes) and coulure (fruit set has failed for a high prop of flowers)
- During summer- can reduce ripening of fruit bc of excess vegetative growth
- Good to have mild water stress right before veraison, reduces growth of shoot tips and allows for ideal grape ripening **
- Close to vintage - grapes swollen w water reducing concentration, can split and encourage disease; plus makes soils difficult for working the harvest
What management options exist for untimely rainfall?
- choice of site, condition of soil, whether or not to grass the land between rows, adequacy of drainage can MITIGATE some of the effects
- Monitoring weather forecasts to make decisions on timing (early harvest)
What are the effects of freeze on the vine?
- temperatures below -20C/-4 F can seriously damage or kill the vine
- Graft is most at risk, followed by canes or cordons
- affects strongly continental climates such as parts of Canada, WA State and China
What management options do growers have to protect against freeze? Summarize each
- Site selection
- Hillside sites can be up to 9F warmer than valley floor
- Large bodies of water moderate cool climates (ie Finger Lakes)
- Where snow settles more thickly can insulate vine - Choice of varieties
- Cab Franc, Riesling more resilient against freeze (FLX, Long Island)
- Hybrids of American and Mongolian vine species are winter hardy - Vine protection
- Soil insulates vine, so building it up (hilling up) around vine graft
- Burying vines (expensive)
- Keep several trunks as backup for those killed in winter
Explain how frost occurs and its effect on vines.
Frost happens when air below 0C/32 F accumulates at ground level, freezing the water in the vine’s growing buds and shoots. If happens to newly burst buds or young shoots, yields can be decimated.
Cool climate areas are vulnerable because vine doesn’t start growing until mean air temp of 50F has been reached.
Warmer areas affected bc vine will have started growing and will be damaged by frost.
Secondary buds can produce more shoots but these will be less fruitful and will take longer to ripen
Compare the two types of frost
Advective frosts are caused by large volumes of cold air moving from very cold areas, while radiative frosts are caused by sudden drops of temperature on still, cool nights where cloud cover prevented too much heat from accumulating during the day, so not much was released at night.
Plus windless nights allow layer of freezing cold air to develop just above soil.
How can grape growers reduce the risk of frost?
- site selection - avoid frost pockets, choose hillsides where cold air does not accumulate as easily as low valley floors
- Delaying pruning postpones budburst until warmer months
- Choose late-budding variety (like riesling)
- Train vines high off ground because coldest air is near ground
- Bare soils between vines (rather than cover crops) absorbs more heat during the day and radiates this heat at night
How can grape growers combat frost? What are the adv/dis of each method?
- Water sprinklers, either specifically for frost or as part of irrigation system. Water freezes around plant and releases heat, protecting the buds, shoots, etc from frost. (DIS Cost of equipment and water) ONLY METHOD THAT CAN COMBAT ADVECTIVE FROSTS
- Wind machines - 4-7 m high fans that pull warm air from above to ground level. There needs to be a warm zone of air 10m above ground 5-9 F, called an inversion layer. (DIS very expensive, but may be worth it if radiation frost may damage vines once every five years)
- Helicopters - same effect, they are expensive but worth it if risk is severe but short term
- Oil or propane gas burning heaters, wax candles (DIS high cost of fuel and labor, low efficiency, contribution to air pollution)
Explain the risk of hail and its effect on vines.
Hail are pellets of frozen rain.
During spring/early summer, hail can damage and rip young shoots and leaves
Ripening grapes can be damaged and become point of entry for diseases.
Yields can be severely damaged in current and following growing season. If early enough, vine can reshoot from existing buds.
It is a localised events. Happens in warmer months.
How can growers protect against hail?
- Firing rockets into thunderclouds with silver iodide to cause rainfall instead of hail
- Netting (causes shading so you need high sunlight levels, i.e. better in Mendoza than Burgundy)
- Own plots in different areas (bc hail is localized)
- Crop insurance
What are the effects of sunburn on the vine?
Sunburn is caused by prolonged exposure to sun because grape transpiration is more limited, so they get hotter more quickly and burn.
- Grapes change color, become scarred and can die
- Impact on quality: bitter taste, increased chance of rot
- Need to be sorted out and this reduces yields
How can a grower manage sunburn risk?
- When designing vineyard, keep row orientation and aspect in mind - avoid east-west orientation, where grapes are exposed to intense afternoon sunshine
- Canopy management, shading
- Additional irrigation to reduce water stress and chance of sunburn
- Agricultural sunscreen spray, shading with cloth or net
Discuss the risk of fires
- Increasingly seen in parts of Australia, California, Chile and other hot and dry countries. Especially w warmer, dryer weather from climate change.
- Cover crops and mulches can provide fuel (bio, org viticulture susceptible)
How can growers protect against fires?
- Fires are out of human control, difficult to prevent - vineyards should just be aware of risk if they are near woodland, pastures or crops that provide fuel
- Install fire detectors and sprinklers
- Install and maintain a water tank
- Provide employee training
How does smoke taint affect the vine?
- Smoky or plastic aromas in final wine from smoke in vineyard
- ** effect on fruit increases in period from véraison onwards - these aroma compounds from smoke are absorbed by grape and bind to sugar, so they only appear after fermentation
How to manage smoke taint
- Musts can be testes analytically or by micro vinification to asses extent of problem
- Mitigate effect of smoke taint- hand harvest, gentle or whole bunch pressing, lower ferment temps, reduced maceration times reduce uptake of these compounds
- Flash detente , reverse osmosis **
- Blending with unaffected wines (plus the above)
Explain phylloxera’s effect on the vine.
Phylloxera feeds and lays eggs on roots of grapevines
They harm vines by damaging roots and disrupting uptake of nutrients and water. Also makes them vulnerable to further infection from other bacteria and fungi.
First plants are weakened, then vines die
What are the symptoms of a phylloxera infestation?
- Vines die of drought in patches
- Vine roots are covered w the insects surrounded by yellow eggs
- Swellings on older roots
- Pale green spots under leaves
- Slow shoot growth, then leaf yellowing after 3 years, then plant dies around 5 years
What is the history of phylloxera?
It was identified in Europe in 1863, having been accidentally introduced from the USA on roots of imported vines.
It spread rapidly and destroyed 2/3 of the European vineyard area in late 19th century.
European grapevine V. vinifera had no natural defence so succumbed rapidly.
During this time it was also noted that vineyards on sandy soil were immune to phylloxera.
Solution has been to graft V. vinifera onto American rootstocks to combat disease.
