What’s in a name? Phosphonates as fungicides

Phosphonate fungicides have very good efficacy for Pythium diseases and other diseases caused by oomycete fungi when applied preventatively; but are thought to have poor efficacy when applied post-infection (after disease symptoms and signs are apparent) see picture above --Effects of reagent-grade potassium phosphite
(H₃PO₃) and potassium phosphate (H₃PO₄) on symptom
development of Pythium blight of creeping bentgrass.
Potassium phosphite has good efficacy against this
disease when applied preventatively.

Literature cited

1. Adams, F. and J.P. Conrad. 1953. Transition of phosphite to phosphate in soils. Soil Science 75:361-371.
2. Anonymous. 2005. Greenbook turf and ornamental reference for plant protection products. Vance Communication Corp., New York, NY.

The following article provides some good information about phosphorus acid fungicides.

This term “phosphorous acid” should not be confused with phosphoric acid or 
phosphorous (P), a fertilizer component. In fertilizers, P is normally found in the form of 
phosphoric acid (H3PO4), which readily disassociates to release hydrogen phosphate 
(HPO42) and dihydrogen phosphate (H2PO4-). Both of these ions may be taken up by 
the plant and are mobile once inside the plant. Phosphorous acid is H3PO3. A single 
letter difference in the name of a chemical compound can make a major difference in its 
properties. Phosphorous acid releases the phosphonate ion (HPO32-; also called 
phosphite) upon disassociation. Phosphonate is easily taken up and translocated inside the 
plant. Phosphorous acid does not get converted into phosphate, which is the primary 
source of P for plants.  

Because phosphorous acid and its derivatives do not get metabolized in plants, they are 
fairly stable and probably contribute little or nothing to P nutritional needs of the plants. 
Some researchers have investigated the ability of phosphorous acid to act as a nutrient 
source for plant growth and found that P-deficiency symptoms developed with 
phosphorous acid as a sole source of P. This means that although phosphorous acid can 
control diseases it is not a substitute for P fertilization. The inverse is also true: phosphate 
is an excellent source of P for plant growth, but is unable to control diseases other than 
improving the general health of the crop. So applying high amounts of P fertilizer will not 
work as a disease control measurer. 

Researchers have found that phosphorous acid fungicides are especially effective against 
Oomycete pathogens, such as Phytophthora, Phythium, and Downy mildews in a number 
of crops. Phosphorous acid has both a direct and indirect effect on these pathogens. It 
inhibits a particular process (oxidative phosphorylation). In addition, some evidence 
suggests that phosphorous acid has an indirect effect by stimulating the plants natural 
defense response against pathogen attack. This probably explains the much broader 
spectrum of activity observed in fungicide efficacy trials in small fruit crops in Michigan. 
We found, for instance, that ProPhyt had efficacy against Downy mildew, Phomopsis,



The phosponate ion is highly systemic and fairly stable in plants. The systemic activity 
allows them to be applied as foliar fungicides for prevention of Phytophthora and 
Phythium root rot

Since these fungicides are actually 
in salt form, care must be taken not to exceed a certain concentration as crop injury may 
result. In addition, if the concentration is too high, the pH may become so low and result in crop injury



Source: Michigan Fruit Crop
Advisory Team Alert, Vol. 20, No. 5, May 10, 2005

Phosphorus Compounds

Fundamental understanding of phosphorus behavior is a key to solving environmental problems of plant, animal and microbe nutrition, eutrophication, corrosion, and geochemistry. Researchers of such problems nearly always assume that phosphorus in natural systems occurs exclusively in the +5 oxidation state as orthophosphate, polyphosphates, organophosphates, and paniculate phosphates. This assumption has never been explicitly proven.

Phosphorus is unique among the major nutrients (carbon, oxygen, nitrogen, phosphorus) in that it is often assumed to lack a gaseous species for atmospheric transport. However, the recent work of Glindeman et al. (1996a, 1996b, 1996c, 1999) and Han et al. (2000, 2003) unambiguously confirmed that volatile phosphine gas (i.e., hydrogen phosphide or PH3) can be detected in the earth’s atmosphere at trace levels. Several sources of phosphine have been also identified by these authors. Unfortunately, perhaps because of the erroneous assumption that phosphorus is nonvolatile, study of total transport through this mechanism has received minimal attention, and all atmospheric phosphorus transport is assumed to be via phosphate dust.

Atmospheric transport of phosphorus is significant. Pierrou (1979) estimated that atmospheric fallout of phosphorus is in the range of 3.6-9.2 Tg (1 Tg = 10^sup 12^ g) P/yr for terrestrial ecosystems (6.3-12.8 Tg P/yr for the earth), and Graham and Duce (1979) attempted to quantify P flux from land to the atmosphere and estimated to be 4.3 Tg P/yr. If this phosphorus was uniformly dissolved in the world average annual rainfall of about 400 χ 103 km^sup 3^, it would suggest an average phosphate concentration of about 10 ppb in rainwater. The potential importance of atmospheric phosphorus loading to oligotrophic lakes was seemingly confirmed by Lewis et al. (1985), who quantified soluble phosphate in rainwater to remote mountain lakes and determined it accounted for 25% of the total annual phosphate flux to the watershed. Interestingly, this phosphate was not associated with dust or pollen. Atmosphere input of soluble P to the coastal ocean was estimated to be 12 10^sup 10^ mol P yr^sup -1^ (Benitez-Nelson, 2000). This is about 10% of dissolved inorganic phosphate from rivers (Duce, 1986; Delaney, 1998). The issue of atmospheric phosphate is discussed in later sections in light of the results of Glindeman et al. (2003).

The phosphate industry directly and indirectly produces many reduced phosphorus compounds. The United States is the largest producer and consumer of phosphate rock in the world. In 1997, the marketable production of phosphate rock in the United States was 32% of the world total production (United States, 45.9 million metric tons; world total, 143 million metric tons). In 2001, the marketable production and sale of phosphate rock decreased worldwide due to decreased demand for fertilizer (USGS, 2001), and the U.S. share of production dropped to 25%.

Phosphorous Acid Fungicides and Phosphorus Nutrients

Phosphites and Phosphonites are alkali metal salts of phosphorous acid and sold as fungicide that control a number of crop diseases particularly those caused by Phytophthora spp. Fosetyl-Al the active ingredient in Aliette is an example of a fungicide in this class that is registered on several crops in Canada for the control of diseases caused by Phytophthora. There are several other different metals salts of phosphorous acid sold as fungicides in the US that are not available in Canada. Fosetyl-Al, was one of the first phosphorous acid type fungicides developed that can move both up and down in plants. Once inside the plant, it is broken down rapidly into phosphorous acid, which is stable but extremely soluble in water and toxic to many Phytophthora species.

Phosphorous acid type fungicides works in two ways. They act directly on the invading fungus to stop its growth and sporulation. They also act indirectly by stimulating the plant to activate their own defense system, thus helping to prevent future infections.
 Plants that have their defense system activated prior to invasion by a pathogen can defend themselves much more effectively.

There is no evidence that phosphorous acid type fungicides can be used directly by plants as a source of nutritional phosphorus. It is possible that when these products are applied to plant root systems or in the soil, soil microbes could convert these compounds to phosphate which would be available to the plant as a phosphorus nutrient. This is a slow process and the amount of phosphate produced would not be sufficient to satisfy the phosphorus requirements of plants. There is evidence however that phosphorous acid type fungicides may actually intensify the deleterious effects of phosphorus deficiency by 'tricking' deprived plant cells into sensing that they are phosphorus sufficient, when, in fact, their cellular phosphorus content is extremely low. Therefore, it is a good idea to make sure that the plants are not deficient in phosphorus prior to using a phosphorous acid type fungicide

In contrast to phosphites and phosphonites, the form of phosphorus plants take up as a nutrient is known as orthophosphate. Fertilizers containing phosphorus are water soluble and once they dissolve, orthophosphate is available for uptake by plants. Following application to the soil, orthophosphate is prone to fixation reactions after which it is no longer available to plants. At lower pH, it forms insoluble salts with aluminum and iron. At higher pH, it reacts with calcium. Either way, these forms are not available to plants, which is why limiting the exposure of phosphorus fertilizer to soil by banded application is a common practice.

Traditional use of areca

: SANTAL: (i) a patient of small pox is given to eat the areca nut when the pustules subside; (ii) a mixture for biliary colic is prepared with areca nut as a constituent; (iii) an ointment for chancre and syphilis is made by pestling areca nut with the root of Gymnema hirsutus, leaf of Piper betel and then cooking the same in mustard oil or butter; TRIBALS also use this plant in rhagadas, venereal sores, syphilis, dysentery, cholera, small pox and for fractured bones.
References to this plant are found in the BHAGVA TA along with the plants of Musa paradisica and Borassus fIabellifer. CHARAKA SAMHITA : Fruit: useful in the diseases caused by bile; SUSHRUTA SAMHITA : Fruit: beneficial in the diseases caused by phlegm; but overuse of this may distort voice of a man; CHACRADATTA : Paste of unripe fruit: may be used as liniment; Extract of unripe fruit: useful in small pox; HARITA SAMHITA : sesame oil in which extract of unripe fruit has been boiled should be used; A YURVEDA : various preparations of unripe and ripe nuts are useful in toothache, pyorrhea, gum diseases, in treatment of worms, while extract of young leaf mixed with mustard oil is useful as liniment in rheumatism; BRAHMAVAIVARTA PURANA : brushing the teeth with twig of this plant is beneficial; AGNI PURANA : (i) immortality can be attained by consuming decoction of this plant along with the powder of root, bark, leaf and fruit of margosa and juice of Wedelia calendulacea; (ii) alkaloids of this plant are beneficial medicine.

ARECA Crop management

Fertilizer recommendation: for areca  plant  
Chemical fertilizer recommendation /plant/ year
100g of N (220g urea)


40g of P2O5 (200g rock phosphate)


140g of K2O (225g muriate of potash)


Should be applied in two split doses


Organic fertilizer
12 kg each of green leaf and compost/plant/year


Weed Control
Research in India has shown that cultivations free of weeds gives better yield


Mulching
Mulching is a regular operation practiced in areca nut gardens in India. It keeps the plant base moist, reduces erosion and keeps the weeds under check. Chopped areca leaves and husks, grass or dry leaves are used for mulching.

What is pH?

Acidic and basic are two extremes that describe chemicals, just like hot and cold are two extremes that describe temperature. Mixing acids and bases can cancel out their extreme effects; much like mixing hot and cold water can even out the water temperature. A substance that is neither acidic nor basic is neutral.
The pH scale measures how acidic or basic a substance is. The pH scale ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic. A pH greater than 7 is basic.
Pure water is neutral, with a pH of 7.0. When chemicals are mixed with water, the mixture can become either acidic or basic. Vinegar and lemon juice are acidic substances, while laundry detergents and ammonia are basic. Chemicals that are very basic or very acidic are called “reactive.” These chemicals can cause severe burns. Automobile battery acid is an acidic chemical that is reactive
The pH scale is logarithmic and as a result, each whole pH value below 7 is ten times more acidic than the next higher value. For example, pH 4 is ten times more acidic than pH 5 and 100 times (10 times 10) more acidic than pH 6. The same holds true for pH values above 7, each of which is ten times more alkaline (another way to say basic) than the next lower whole value. For example, pH 10 is ten times more alkaline than pH 9 and 100 times (10 times 10) more alkaline than pH 8.

Agribiotech conclution -PH value is very very important in agriculture fertilizer and fungiceides becuse -each whole pH value below 7 is ten times more acidic than the next higher value