Soybean Rust Fungicides

1. Soybean Rust Fungicides Alan Henn Extension Plant Pathologist Mississippi State University 662.418.9697

3. What is a Fungicide ? Something that kills fungi Some “fungicides” don’t really kill the fungus, but just slow its growth until the chemical is gone fungistatic

4. Fungicides belong to groups of a number of chemical classes Generally a class is a group of compounds built around the same type of chemistry The types of fungi each class will control will be similar (all sterol inhibitors - SBI’s); are great on powdery mildew) Resistance will be similar. Cross resistance. The rate range for compounds will be similar

5. Reducing / Delaying Inoculum Using Fungicidal Chemicals

6. Fungicide Classifications Classified as “protectants/contacts” or “penetrants*” varies with chemical class Protectants: stay on leaf surface – may spread out some Protectants or contacts usually inhibit the fungus multiple ways Penetrants: penetrate into the leaf; Usually inhibit the fungus by one mechanism only Some move only within the leaf : Locally Systemic Some locally systemic fungicides move from the side of the leaf where deposited to the other side of the leaf: translaminar Others enter the xylem and move upward: acropetal

7. Protectant/Contact Fungicides Provide a chemical barrier to the fungus Little use post-infection Require excellent coverage of the foliage Have multiple sites of action Performance affected by: weathering (rainfall, temperature, sunlight, etc.) Plant growth, pruning High rates with short residual - Requires frequent applications

8. Penetrants: all other rust Fungicides

10. “Penetrant*” Fungicides Absorbed by foliage. Locally systemic: Usually through xylem. Translaminar movement. Cell to cell. Example: Quadris, Headline, most azoles Fully systemic: Move through xylem and phloem. Example: Ridomil

11. Curatives and Eradicants Penetrants may be may be “curatives” or “eradicants” Both are really poor words which must have been thought up by marketing types Curative: the ability to inhibit or even kill the fungus which as already entered the plant Eradicant: the ability to stop the fungus inside the plant form producing spores – at this time no US approved SBR fungicides are eradicants

12. Strobilurins Pyraclostrobin (Headline), Azoxystrobin (Quadris), Trifloxystrobin part of Stratego) Preventative application is KEY Provide control of germinating spores prior to infection Little control of existing infections once in plant Offer residual control to prevent new infection New foliage requires new application on some

14. Heritage Fungicide Uptake and Movement foliar uptake slow but steady; typically less than 10% - 20% of applied in 24 hr., 35% after 7 days 85% of A.I. taken up by the leaf is still available in the leaf after 10 days even distribution throughout leaf; does not accumulate at leaf tips or margins translaminar movement (from upper to lower leaf surface) xylem systemicity in emerging leaves not present at application uptake is upwards by roots, leaves, stems, etc.

15. Quadris slow uptake vs. DMI fungicides

17. The Imidazole Problem EPA has been very reluctant to register members of the imidazole (triazole) family for ANY food use Concerns: 1) long-lived secondary breakdown residue – and 2) endangered species Task Force in effect called the Triazole task force to review these concerns – hopefully report this spring Myclobutanil and Propiconazole both OK'ed for residue ~ 1 yr ago – thus Section 18 approvals Many other azoles have no residue data!

18. Propiconazole Propimax Tilt Bumper

20. Chemistry Chemical class: Triazole Signal word: WARNING Appearance: Clear yellow-amber liquid Odor: Mild aromatic solvent odor Specific gravity: 1.09 g/cm³ Solubility in water: 0.1 g/L @ 20° C

21. Precautions/Safety REI: 24 hours PPE requirements for early reentry: Coveralls; chemical-resistant gloves; shoes plus socks; and protective eyewear.

25. Tetracoanazole Originally to be marketed by Sipcam Agro Falling out on part of manufacturer of active ingredient Now to be marketed by Valient under name Domark

26. Tetracoanazole Domark Systemic azole “Curative” and some “Eradicant” ability Probable use about 10 -14 oz/A Cost/A $12.42 (not including application costs)

27. Other Imidazoles Which may Receive Section 18 ApprovalDon't your breath Metconazole Flusilazole Flutriafol Cyproconazole Prothiocanazole

28. Fungicide Resistance Action Committee (FRAC)www.frac.info For Strobilurins (azoxystrobin, pyraclostrobin, trifloxystrobin) Good IPM Practices involve utilizing all available management tools when dealing with this or any disease. Also, good fungicide resistance management practices as listed above indicate the frequency of use recommended for different pesticide chemistries. These practices should be followed between blocks and within blocks of soybeans. Other alternate chemistries that may be worth considering are boscalid, chlorothalonil, mancozeb and maneb. Mixtures of fungicides should combine different chemistries. Good IPM Practices involve utilizing all available management tools when dealing with this or any disease. Also, good fungicide resistance management practices as listed above indicate the frequency of use recommended for different pesticide chemistries. These practices should be followed between blocks and within blocks of soybeans. Other alternate chemistries that may be worth considering are boscalid, chlorothalonil, mancozeb and maneb. Mixtures of fungicides should combine different chemistries.

29. What and When If the crop is already infected with or exposed to rust rust, use an active ingredient ending with “zole” (or myclobutanil) especially tebuconazole If the crop is not infected or exposed, use a strobilurin, or use a strobilurin as the second application – 20 days after the first If light disease pressure or late arrival, 3rd spray not needed– otherwise strobulirin or your choice unless previous spray was an azole