Managing crop recovery after flooding - grapevines
Note number: AG1435
Published: February 2011
Flooding of vineyards can result in several consequences. At the extreme, vines and trellis systems can be washed away or flattened by the water and debris moving across the vines. In such cases it may not be worth attempting to retrieve a crop in the current season but to look toward reinstalling the trellis and standing vines up for pruning in the winter.
If the soil remains waterlogged (saturated) for extended periods, plant health will be affected in a number of ways. In waterlogged soils the air between the soil particles is replaced by water. A lack of oxygen in the soil over an extended period will result in root and plant death. Flooding may also cause the leaching of nutrients, loss of mulch material and crusting (slaking and dispersion) of the soil, and these effects will require management. In addition, shallow, stagnant water can heat up quickly in hot weather and kill plants so it is important to remove excess water as quickly as possible.
Another consequence of flooding is complete covering of the vine. If only for a short period (<1 day) then there will be minimal impact on vine function. Large amounts of debris can block access to vine rows and this will need to be cleaned out before access can be gained. Erosion of soil may have also occurred in places and these areas will need to identified and remedied before driving along vine rows. The main result of inundation is debris in the fruit zone which should be carefully removed (don't damage the fruit) so it does not end up in the harvested fruit. Avoiding damage to fruit will reduce the potential for bunch rots to develop. Flooding could also leave a fine layer of silt on the leaves and this may reduce photosynthesis and vine productivity. The crop load and ripening process should be monitored closely and adjusted to avoid any undo delay in ripening.
The full impact of inundation or waterlogging will not be apparent for some time after the event so ongoing monitoring is important to manage vine health and identify issues. Waterlogging may continue particularly in clay soils and duplex soils with a shallow impermeable clay layer below the surface soil. Digging a hole or installing a test well can help monitor the water table depth and hence the degree of waterlogging. Areas remaining waterlogged for several weeks, need to be identified for remedial action in the future, e.g. by installing drainage.
In grapevines, pot experiments have shown vines will tolerate 3 to 7 days of soil waterlogging before showing signs of reduced growth. Longer periods of intermittent waterlogging (3 days waterlogging every 14 days for 18 weeks) reduced total growth of the vines by 36%. Vines have also been shown to have a lower rate of photosynthesis even after waterlogging has ceased.
The timing of waterlogging can also be important. Periods of active root growth, between flowering and veraison and after harvest, are very sensitive to lack of oxygen. Nutrient uptake is also greatest before veraison and drops away in the period between veraison and harvest. Thus waterlogging before veraison will have more impact than after veraison.
Symptoms of waterlogging stress include wilting and chlorosis of leaves due to lack of nitrogen and shoot dieback. The vines will not be accumulating nutrients while waterlogged consequently there will be potential to affect yield the following season and there may be some root death. For the current crop, berry size and bunch weight may be reduced. Extended waterlogging for more than 10 days will kill the roots.
Some soils, especially those with a high clay content, can become compacted and form a surface crust after heavy rainfall and flooding. Flood waters can also deposit a fine clay layer or crust on top of the soil which may prevent oxygen and water penetration of the soil.
Waterlogging is also known to exacerbate the impact of salinity. Salts in the subsoil are moved into surface soils by flooding and rising water tables become highly concentrated and damage vine roots as the soil dries. When root function is impaired by a lack of oxygen the plant has difficulty keeping sodium and chloride out of the roots and the vines end up accumulating more salt than normal. Other nutrients such as nitrogen, phosphorous and calcium can have their uptake inhibited under waterlogged conditions.
Whilst grapes are relatively more tolerant of waterlogged conditions than many fruit trees and olives, some grape rootstocks are quite susceptible to waterlogging. Richter 99 is quite sensitive to wet feet whereas Schwarzmann and ungrafted vines are relatively more tolerant. Root rots are another potential problem with waterlogging with the main issues being Phytophthora spp., Armillaria spp., Pythium spp. and Cylindrocarpon spp.
What should I do?
The best defence is to drain or pump water from the vineyard within 3 days. Where possible a spoon drain dug in the centre of the traffic line will help surface drainage.Where flooding is landlocked, a sump can be dug to assist pumping. The water will also be removed by transpiration by weeds and through evaporation from the soil largely assisted by wind movement. A trimmed canopy and a permanent sward in the vineyard would facilitate the drying process. Where vine roots have been damaged by waterlogging and root rot, irrigation should be scheduled carefully to allow for the reduced root uptake and avoid water stress in the vines once the water has drained away.
It is important not to drive on the vineyard while the soil is very wet because that will result in compaction of the soil. Low flotation tyres are available which can be fitted to tractors and spray units to reduce compaction of the soil. There may be issues with crusting of the soil and hard setting but it is not advised to undertake any cultivation or mechanical activities until the soil dries to an adequate level. If there is likely to be a heavy clay layer, which may inhibit drainage and result in a perched water table, it is advisable to treat the area by applying gypsum (the rate should be determined by a soil test) to the vine line.
If the soil has set hard, once it is dry (at field capacity) a "one-off" light cultivation may be desirable to break up the compaction to allow water and oxygen to penetrate. However care should be taken for cultivation has the potential to pulverize the soil and further damage soil structure.
If sections of the vineyard are likely to require re-planting a soil test before replanting is advisable so any soil amendments, e.g. gypsum, can be added while there is a clear area. An organic mulch, e.g. straw, spread on the vine line will reduce crusting plus improve water penetration, aeration and drainage of the soil profile. Farmyard manure and organic mulches applied to the vine line can encourage beneficial fungi antagonistic to Phytophthora root rots.
Re-sowing the cover crop or permanent sward between rows is desirable over the coming autumn and winter if it has been damaged by the flood. This will assist in replacing organic matter that may have been lost and result in improved soil structure and aeration A cereal crop such as oats or a medic are suitable cover crops while cereal crops will be easier to establish and will provide more bulk.
Heavy rainfall and flooding can cause nutritional problems for nitrogen, potassium and boron are prone to leaching and levels are likely to be reduced. Fertiliser applications should be adjusted to make up for any shortfalls, however adjust rates with caution as over application will also need to be avoided. It will be essential to undertake petiole analysis the following season when vines are flowering and have the results interpreted by a consultant to tailor fertiliser applications to the vines needs. Silting may also cause de-nitrification of the soil by bacteria as a result of less oxygen being present in the soil and becomes significant when the soil has been waterlogged for 36 hours or more.
Apart from root rot issues, many diseases are more active in wet, humid conditions. Where water is laying or soils are waterlogged, humidity will be higher adding to disease pressure and this should be factored in when considering disease control programs. Vines should be monitored closely for increased presence of fungal diseases. Cultural management techniques to minimise the outbreak of diseases should also be considered, e.g. crop load adjustment, leaf plucking, canopy topping, and bunch thinning. Any treatment should not damage the bunches as to do so would greatly increase the incidence of bunch rots.
A list of pesticides registered for grapevines and the withholding periods is available from the Australian Wine Research Institute website. However, always check with the winery you supply grapes to, as to the suitability of intended chemical treatments. Waterlogged soils are also likely to increase the disease pressure from the root pathogens Phytophthora and Armillaria root rots and vines should be monitored for dieback for some time afterwards. Armillaria is more likely to be a problem where vineyards have been recently established following the clearing of native bush. Hilling up of the soil under the vine row helps facilitate drainage away from the vine roots but do not cover any graft unions with this practice.
Soil diseases are difficult to identify so suspected soil and root samples should be taken for disease identification which can be carried out by the Crop Health Service (03 9210 9222). For more information see, Phytophthora Root and Trunk Rot of Pome and Stone Fruit AG0191 and Armillaria Root Rot AG0155.
Lovett, J (January 2011) Managing horticulture crop recovery after floods and waterlogged soil, DEEDI, Qld.
Washington. W.S (July, 2010) Armillaria Root Rot, Agriculture Note AG0155, DEPI, Victoria.
Adem, H (January, 2010) Phytophthora Root and Trunk Rot of Pome and Stone Fruit, Agriculture Note AG0191, DEPI,Victoria.
Correct diagnosis is essential for effective pest and disease control. A commercial diagnostic service is available at the AgriBio Bundoora. For further information, phone Crop Health Services on (03) 9032 7515.
For further information on registered chemicals, phone our Customer Services Centre on 136 186.
This Agriculture note has been prepared by Rob Dimsey, John Whiting and Harold Adem, Farm Services in February 2011.