BOTRYTIS
Botrytis is still one of the most important grape diseases in New Zealand. Incidence and severity depend on a number of factors and vary from year to year, and from region to region. Certain varieties are more susceptible than others.
In the last few years a lot of attention has been given to canopy management as a tool to reduce the problem, and few people would dispute the importance of canopy management in relation to Botrytis control.
AgConsult is involved in some new areas where targeted management can further strengthen Botrytis control.

Inoculum Reduction
Reducing inoculum in the vineyard will reduce disease pressure. Reducing spore numbers overwintering in the vineyard shows promise, trials on other crops have shown this strategy can reduce Botrytis infection at flowering. Spore numbers can be reduced by maintaining good hygiene in the vineyard. Trials show they can also be reduced by accelerating the breakdown of substrate on the vineyard floor on which the spores overwinter, and possibly by enhancing competition form other organisms on the vineyard floor.

Strengthening the Vine's Own Defences
This is a very exciting area. Grapevines, like most plants, have systems in place to deal with pathogenic attack (the plants immune system). In most cases the plant responds to external stimuli (like pathogen attack) by producing a number of different substances that in turn activate a number of different defence mechanisms. After the initial stimulus it will take some time for the defence mechanisms to get up to "full strength", which means that it may be too late to control the pathogen. Using natural compounds we can elicit these defence responses, in effect preparing the plant for pathogen attack. This has been likened to "vaccinating" the plant. In the case of grapevines, the elicitors increase levels of resveratrol, one of the main phytoalexins identified in the immune response. Resveratrol has also been associated with some of the health benefits of drinking red wine.

Promoting Good Biofilm or Phyllosphere Activity
The phyllosphere or biofilm is the aerial surface area of plants (leaves, stems etc), the complement of the soil equivalent rhizosphere. These surface areas are host to many different microorganisms which on healthy plants colonise a large part of the biofilm. Promoting good biofilm activity will help control pathogen attack. Beneficial organisms can inhibit pathogens through production of inhibitory substances, competition for nutrients and or space. There are several ways beneficial biofilm activity can be enhanced, and in vitro trials have shown the effect of good biofilm activity on Botrytis is very promising.
We are involved with further research and trials in all three areas.



PHYLLOXERA
In recent months, the presence of Phylloxera has been confirmed in one Central Otago vineyard. Although the Central Otago wine growing area is relatively small, it is growing fast and has potential to produce some top quality wines. Phylloxera is already present in many other grape growing areas, but in most cases phylloxera resistant rootstock has been introduced to combat the problem. There are still a number of own-rooted vineyards however where phylloxera is a problem.
Conventional treatment is based on the use of fumigant type products that can reduce phylloxera numbers significantly, but long-term success rates are not encouraging. In addition, the effects of these products may also impact on beneficial bacteria and fungi in the soil, which in turn can affect vine performance.
Organic type management aimed at maximising soil and vine health appear to have the potential to reduce the impact of phylloxera on vines.
Mostly these approaches maximise biological activity and competition in the soil, increase beneficial biological activity in the rhizosphere, and strengthen the vine's own defence system.
Many of the practices used are very similar to organic management practices in vineyards, although not all would fall in that category.
These findings are based on work by Don Lotter (as PhD student at UCDavis) and our involvement with trial work in New Zealand and California in association with Bio-Start Ltd.
It is important to point out that there is no evidence that the organic Phylloxera control alternatives kill or even decrease phylloxera numbers in the soil, at least not in the short term.
It appears most of the impact of Phylloxera damage to roots is through secondary infection: after the initial damage caused by phylloxera, the damaged root is more likely to be invaded by pathogenic fungi like Pythium and Fusarium. It are these fungi that most likely do the real damage by "clogging up the root channels".
The impact of management practices that promote soil biological activity may be to a large extent by minimising the secondary infection and damage. Soils with good soil biological activity and diversity have a significant suppressive effect on pathogens like Fusarium and Pythium.
Other mode of actions may be (there are others but that would be outside the scope of this text):- Under organic management vines are likely to have stronger defence systems to pathogenic attack (SAR Systemic Acquired Resistance).
- The presence of PGPB -Plant Growth Promoting Bacteria and other beneficial rhizosphere microbes increase root activity/growth, which can compensate for the damage done by phylloxera.

Ongoing trials in this area are taking place.





NATURAL ELICITORS
Plants respond to external stimuli. When attacked by for instance a fungal pathogen on the leaves, receptors on the leaves will recognise the pathogen attack and set in motion a series of defensive actions. There are a number of different mechanisms that the plant can use to defend itself. These include the pre-existing systems (for instance wax and cuticle covering epidermal cells), inhibitors released by the plant to deter pathogens and others. And there are mechanisms that respond to pathogen attack through recognition of the pathogen by the host plant. These are the induced structural and biochemical defences.
As a result of pathogen attack the plant can activate cytoplasmic defence reactions, it can change/develop cell wall structures, it can develop hypersensitive defence reactions or activate histological defence structures.
In grapevines part of the defence reaction involves phytoalexins, including a compound called resveratrol. Resveratrol has been identified as one of the main compounds in the plants defence against a number of fungal pathogens like Botrytis, in effect protecting the leaves and fruit from attack as long as resveratrol concentrations are high enough (in the berries they tend to decrease over time).
One of the weaknesses in the plants armour is the delay between recognition of pathogen attack by the vine and the time it takes to build up the defence systems.
Plants that are in an environment where they are challenged frequently by pathogens, develop amazingly effective defence capabilities.
In recent years significant progress has been made in our understanding of these processes.
By "eliciting" the defence response in the plant we can help protect it against future pathogen attack. Some people even go as far as using the term "vaccinating plants"
How can we prime the plants immune system? We can expose the plant to a low dose of pathogen inoculum) or a devigourised strain of the pathogen, but this can still be risky.
There are other ways; there are a number of natural substances that have similar molecular structure as some of the pathogen cell wall fragments, and when applied to the surface of the plant the plant responds as if it is being attacked by a specific pathogen.
Some researchers have worked with some of the signal compounds that play a role in the defence response, Salicyclic Acid derived compounds fall into this category.
AgConsult has been involved with work on grapevines and other plants using a number of different natural substances to elicit plant defence responses.
Some of these compounds and products have shown to lift resveratrol levels in grape vines significantly, creating considerable interest. Work on commercialising some of these substances is underway.



MYCORRHIZAS
Mycorrhizas are symbiotic relationships between fungi and plant roots (the term means literally 'fungus root'). Perhaps more than 70% of the species of higher plants have these relationships, and so do many ferns and some mosses. They are as common on crop plants (cereals, peas, tomatoes, onions, apples, strawberry, etc) as in wild plant communities and in several cases they have been shown to be important or even essential for plant performance.

Generally, mycorrhizas are symbiotic (mutually beneficial) relationships, in which the fungus obtains at least some of its sugars from the plant, while the plant benefits from the efficient uptake of mineral nutrients (or water) by the fungal hyphae.

Mycorrhizal fungi promote good plant nutrition by obtaining nutrients from the soil, and exchanging these nutrients with the plant for carbon. In addition, mycorrhizal fungi can physically protect roots against pathogens and root-feeding nematodes, and improve soil structure by binding soil aggregates in to larger, water-stable aggregates.

The two main types of mycorrhizal fungi are Ectomycorrhizal and Arbuscular or endo-mycorrhizal fungi. Ectomycorrhizas are characteristic of many trees in the cooler parts of the world - for example pines, spruces, firs, oaks, birches in the Northern Hemisphere and eucalypts in Australia. Grapevines form association with both types of fungi, but there is a tendency to find more endomycorrhizal fungi on young vines. When the vines are 4-8 years old, there appears to be a shift towards ectomycorrhizal fungi. This has been linked by some researchers with increased grape quality.

Arbuscular or Endo- Mycorrhizas
Arbuscular mycorrhizas are found on the vast majority of wild and crop plants, with an important role in mineral nutrient uptake and sometimes in protecting against drought or pathogenic attack. It is thought that these fungi colonised the earliest land plants and that mycorrhizal associations could have been essential for development of the land flora.
These fungi can extend up to 10 cm away from the roots, and have access to nutrients that the plant roots do not have. These fungi are particularly efficient in sourcing phosphorus and zinc. In addition they will help increase the plants resistance to certain pathogens.
VAM (Vesicular Arbuscular Mycorrhizal) fungi penetrate the root cells while ecto-mycorrhizal fungi form a mantle around the root.

Ecto Mycorrhizas
The fungi involved are mainly Ascomycota and Basidiomycota, including many that produce the characteristic toadstools of the forest floor. Most of these fungi can be grown in laboratory culture but, unlike the wood-rotting fungi, they are poor degraders of cellulose and other plant wall materials. So they gain most of their sugars from the living plant roots in natural conditions.Ecto mycorrhizal fungi can form long extended hyphae. In one case hyphae were found to extend almost 50 m from the host plant (grapevine).

In ectomycorrhizas the terminal branches of the root system are highly modified - the roots are short and stubby, covered with a mantle (sheath) of fungal tissue, and there are fewer or no root hairs. The fungus takes over the normal nutrient-absorbing role of the root hairs.




Ectomycorrhizal fungi on typical "stubby" roots

Such roots are seen easily if the undecomposed, surface litter is scraped away from a forest floor to reveal the decomposing litter containing a mass of mycorrhizas and their fungal networks.



FERTIGATION
A significant number of vineyards are now set up for fertigation. More than likely this number will increase significantly. The reasons for this increase are varied, they include nutriononal support for newly planted vines, to address magnesium deficiency in vines. Fertigation is very effective in lifting phosphorus levels, and often it is used for postharvest nutrition. Sometimes it is used to provide general NPK support on low fertility soils.
Where growers rely heavily on irrigation, nutrients can be depleted quite rapidly in the drip zone if soils have low fertility. Basically the vines need to source most of their nutrients from a very limited soil volume if moisture levels outside the dripzone are low.
Adding some nutrients to the irrigation water will counteract this depletion and is a good nutritional management tool that can be used to regulate vigour and other parameters.
The down side of fertigation is that incorrect use (type of products, timing, application management) can cause acidification of the soil and other problems.
In our view there is a general lack of understanding around fertigation issues. When to use, where to use, what product etc.
AgConsult can help develop a fertigation program for your vineyard, based on soil and petiole analysis, the fertigation system you are using, vineyard (soil) characteristics, yield/quality desired and other factors.