Agriculture Reference
In-Depth Information
uptake, for example, the use of manures and fertilizers, or improving soil struc-
ture and alleviating soil compaction.
Fumigants such as 1,3-dichloropropene are effective nematicides, especially
for nematodes that survive for several years in the roots of previous crops. Because
nematodes are found at depths to 90 cm, penetration of the fumigant is a po-
tential problem, so proper land preparation before fumigation is important. This
is discussed under Soil Preparation in chapter 8.
Vertebrate Pests
Rabbits and hares (jackrabbits) eat through the bark of vine trunks and damage
the growth cambium. Moles and voles (mainly in Europe), and squirrels and go-
phers (mainly in North America) attack the roots. These pests are primarily a
problem in young vines, which is one of the reasons “vine guards” are used around
the trunks (section 7.5.3). The animals can be controlled with traps and baits.
7.3.3.3
Fungal, Bacterial, and Viral Diseases
Grapevines suffer from a number of diseases, some of which are soil-borne. For
others, soil management can influence the incidence of disease (e.g., mulching and
Botrytis ), or disease control measures can have an impact on the soil. For exam-
ple, powdery mildew ( Uncinula necator ) is not soil-borne, but the disease is con-
trolled by spraying wettable S when the vines are susceptible. Regular use of S
over many years can decrease the topsoil pH (section 5.4.2.2). Powdery mildew
persists on vines in winter and develops under favorable temperatures (22-28°C)
in summer, especially in crowded canopies.
Botrytis cinerea (bunch rot) is favoured by temperatures of 15-24°C and at-
tacks flowers and berries. It is not soil-borne, but survives on mummified fruits,
so that vineyard hygiene is important. However, another canopy disease, downy
mildew ( Plasmopara viticola ), overwinters on leaves in the soil. When tempera-
tures are greater than 10°C for at least 24 hr, spores that are splashed onto the
foliage by rain ( 10 mm), will germinate and infect the leaves. Downy mildew
has traditionally been controlled by Cu sprays (Bordeaux Mixture and other Cu-
based fungicides), which has led to potentially toxic Cu concentrations in the top-
soils of vineyards in the Bordeaux region (section 5.5.2). Another vine disease in
California and Europe is the root rot fungus Armillaria mellea , which spreads from
old oak tree roots. Fungi of the genus Phytophthora cause many root diseases, and
P. megasperma can cause root rot of grapevines, if the vines are waterlogged or
where drip irrigation splashes directly onto the trunks of young vines.
Crown gall ( Agrobacterium tumefaciens ) is a bacterium that lives inside the
vine and infects wounds in the trunk, forming galls that may kill the vine. It is
most severe in cold, moist climates where frosts are common. Although not soil-
borne, Pierce's disease ( Xylella fastidiosa ), a serious problem in parts of California,
is a bacterium hosted by some grasses and sedges that grow along streams. “Sharp-
shooter” leaf hoppers pick up the bacteria, spreading them as they feed in adja-
cent vineyards. Vineyards with permanent cover crops seem to suffer more seri-
ous damage (and vine death). Another disease transmitted by leaf hoppers is
“grapevine yellows” (flavescence dorée), which is caused by phytoplasma organisms,
similar to bacteria, that invade the conducting tissues and may kill young vines.
The Grape Fanleaf Virus (GFLV) and its vector the dagger nematode X. in-
dex are not lethal but cause yield reductions.
7.3.3.4
 
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