Fungicide use in the United States
[6] A tree infected with Phytophthora can either undergo a period of slow decline that may last years or it can suddenly collapse and die in spring with the advent of warm weather.
It is only when cooler temperatures and heavy moisture is present that almond growers are recommended to make fungicide applications specifically for the disease.
[6] Treatments of maneb and sulfur in the early season months (typically spring and summer) have been shown to significantly reduce incidence and severity of rust outbreaks.
Mating among different strains of the fungus occurs shortly after leaf fall with spores developing in the fallen leaves during the winter.
Spring rains cause spores to be forcibly discharged; they can be carried long distances by air currents to flowers, leaves, or young fruit.
While fire blight has always been a concern in eastern apple production, severe outbreaks in the west in recent years have caused growers there to adopt more consistent and vigorous monitoring and management programs as well.
Quince rust is economically important primarily when an extended wetting period with a mean temperature above 10 °C (50 °F) occurs between the tight cluster and late pink bud stages.
[33] This increase in yield as a result of purple spot control has been shown to translate into a net return of $200–400 per acre for asparagus growers .
Stripe rust is now established in California, Idaho, Oregon, and Washington and all other barley areas of the Pacific Northwest are considered highly susceptible.
Over the winter the mummyberry infection incubates in the mummified blueberry fruit that has fallen on the ground and in the spring cup-shaped structures of the fungus begin to grow.
[15] Pseudomonas blight is a bacterial disease that invades the blueberry plant early in the season when tissue is damaged by freezing temperatures.
It is only a superficial effect to the plant but because of the black color of the leaf spots the marketability of a severely infected cabbage crop is low.
[65] Alternaria leaf spot is controlled using the same treatment as downy mildew: applications of azoxystrobin, copper, chlorothalonil, mancozeb, and maneb beginning midseason.
Due to its ability to spread rapidly and destroy entire fields of crops black rot can be considered the most serious disease of the cabbage plant.
The abnormally large roots are unable to properly absorb water and nutrients from the ground and the result is cabbages that are undersized, wilted, and discolored.
Therefore, growers who plant early are advised to use in-furrow fungicides for control: PNCB and iprodione for Rhizoctonia and etridiazole and mefenoxam for pythium.
Early symptoms of garlic rust are small yellow spots on the leaves that soon expand until the leaf tissue shatters and visible pustules emerge.
Diseased bulbs lose their protective dry outer skin, preventing photosynthesis and leaving the garlic prone to shattering when mechanically harvested.
[90] In order to control powdery mildew the same treatment that was recommended in the late 19th century is still used today: regular applications of sulfur every 1–2 weeks.
[64] Each individual spore can produce a fresh pustule on a plant within a week; therefore untreated rust can rapidly reach epidemic levels.
[102] Since white mold affects plants very late in the growing season farmers would often harvest early to avoid losing much of their crop.
[105] Research with chlorothalonil and tebuconazole in the 1990s showed that 4–5 applications of the fungicides on a two-week schedule when vegetative buds are breaking dormancy is ideal for control of EFB.
These growths release spores that infect the lettuce plant with pathogens that slowly move up the stalk, killing tissue as they travel.
[124] Originally the disease was localized to North Carolina and Virginia, but recently Florida and Georgia have begun experiencing higher incidences of the rot.
[126] (Cercospora arachidicola) Spots first appear on the upper surface of lower leaves as faint brown to black pinpoint dots.
[124] Scletotinia blight was first discovered in Virginia in the early 1970s but soon spread to the peanut producing states of North Carolina, Oklahoma and Texas.
[61] The primary modes of dispersal of yellow rust are wind and the splashing of raindrops, making wet conditions ideal for its spread.
The disease harms the plant because when rice infected with kernel smut is harvested it often breaks during the milling process and is rendered useless.
Cultivars were vulnerable to downy mildew, which caused sharp reductions in quality and in select cases complete crop loss.
Heavy rains, low temperatures, and relatively high humidity increase the number of life cycles of the fungus, producing additional spores.
