Welcome to the North San Joaquin Valley Cling Peach Day Sponsored by UC Cooperative Extension

1. Welcome to the North San Joaquin Valley Cling Peach Day Sponsored by UC Cooperative Extension & the California Cling Peach Board

2. Fertilization Guidelines for Peaches Roger Duncan Pomology & Viticulture Advisor University of California Cooperative Extension Stanislaus County

3. Today we will discuss: • Nitrogen • Phosphorus • Potassium • Zinc

4. A good fertility program is based on: • Replacing what is removed with the crop • shouldn’t be based on “what I always do” • Monitoring long term trends with annual tissue samples • Occasional soil samples for gradual changes in soil chemistry. • Yield is already affected by the time you see symptoms

5. Nitrogen Deficiency • Mild deficiency: lack of growth, smaller, pale green leaves with red tinge • N is mobile, shows in old and new leaves

6. Nitrogen Deficiency • As deficiency worsens, leaves get yellower and smaller • May develop red spots

7. Nitrogen Deficiency • Lower N favors good color in fresh market fruit

8. Crop load drives demand for N: • Between 2 – 3 pounds of N removed with every ton of peaches • Perennial structure requires additional ~ 20 lb. per acre • More in high density orchards • Leaves & prunings ~ 60 lb. (80-90% recycled)

9. Approximate N fertilizer requirements for mature peach and nectarine orchards. • Assumes that prunings are not removed from the orchard • 2.69 lbs. N are removed per ton yield • 19 lb for perennial part of tree • 90% recycle of leaves & prunings (~ 9 pounds) • N use efficiency is 70%

10. Excessive N Fertilization Leads to: • Excessive shoot growth • Increased (summer) pruning costs • Excessive shading of lower wood • Shorter orchard lifespan • More brown rot • Poor coloration and delayed harvest (fresh market) • Potential ground water contamination • Regulations

11. Leaf sampling procedure: • June – July • Sample each variety / block separately • Weaker or “different” areas of a block should be sampled separately

12. Leaf sampling procedure: • 60 – 100 mid shoot leaves from current season shoots. • Leaves treated with foliar zinc are not useful to determine zinc status • Trees sprayed with N should not be sampled for at least one week • Analyze promptly or refrigerate

13. Dormant Shoot Sampling: • July sampled leaves too late for current season adjustment and for zinc contamination • Sample 30 – 40 moderately vigorous shoots 10-20 inches long from lower canopy. • Guidelines are for January but fall may give similar results

14. UC Guidelines for Nitrogen in July-Sampled Leaves and Dormant Shoots

15. Nitrogen Fertilizers: • Trees don’t care – N is taken up as nitrate whether organic or inorganic • Nitrate very mobile in soil, leachable • Ammonium less mobile but converted to NO3 within days at warm temps • Nitrification; acidifies soil • Urea converted to ammonium, will volatilize quickly on soil surface

16. Time of Nitrogen Fertilizer Application: • Trees take up almost no nitrogen when leaves are absent. • Nitrogen for spring growth comes from N stored in roots, trunk, shoots. • Nitrogen applied before leaf out is susceptible to loss by leaching and volatilization.

17. Time of Nitrogen Fertilizer Application: • Peaches relatively low users of nitrogen compared to almonds so don’t need to “front load” so much. • Extra earlies (especially May – June fresh market peaches) • Too much N early leads to excessive growth after harvest, poor quality • Late summer applications might be good strategy • Provides N for next year’s crop without excessive post-harvest growth • Foliar urea in fall

18. Foliar Nitrogen Application: • Studies show that 20 – 50% of N can be supplied through the leaves • Urea is cheapest and mostly easily absorbed into the leaf • Up to 50 lbs. of N / acre (100 lbs. urea) can be sprayed per application • Multiple applications OK two weeks apart

19. Foliar Nitrogen Application: • When to spray • October • Before natural leaf senescence • September too soon due to earlier defoliation • If combined with zinc, more N (and Zn) mobilized into storage than if applied alone

20. Phosphorus • P deficiency is very rare in California • Most soils contain a lot of P, most is in unavailable form

21. Phosphorus Deficiency • Lack of spring growth

22. Phosphorus Deficiency • Reddening of new growth in spring • More mature leaves can be darker green than normal

23. Phosphorus Deficiency • Phosphorus deficient leaves turn purple in fall

24. Phosphorus Deficiency • Branches can defoliate and collapse under severe deficiency

25. Phosphorus Deficiency • Some varieties may crack under severe P deficiency

26. UC Guidelines for Phosphorus in July-Sampled Leaves and Dormant Shoots *Previous literature cited 0.10% P as adequate for leaves

27. Phosphorus Fertilization: • Very rarely needed in California peaches • 0.5 – 1.0 lb. P2O5 removed per ton of fruit • 10 – 20 lb. P205 in a 20 ton crop • P is very immobile in soil. Cannot be leached with irrigation or rain. Therefore timing is not important. • Usually drilled 6 -8 inches deep • If fertigated by drip, be careful not plug with calcium phosphate precipitate

28. Phosphorus Fertilization: • Side note – phosphorous acid materials (phosphites) do not supply tree with P • Good for Phytophthora management, not as a P fertilizer

29. Potassium (a.k.a. Potash) • More potassium removed than N • Can influence fruit size • Might be neglected more than it should be

30. Potassium (a.k.a. Potash) • Deficiency usually first seen in early summer • Potassium deficient leaves tend to roll at the edges • Midshoot leaves affected most

31. Potassium Deficiency • Leaves may also be a little pale. Margins may scorch

32. Potassium Deficiency • Fruit set, shoot growth and leaf size is reduced • Fruit size and color are reduced • *Fruit size can be reduced before other signs are obvious

33. Potassium Deficiency • Severe potassium deficiency can lead to defoliation and limb death

34. UC Guidelines for Potassium in July-Sampled Leaves *Probably should be > 1.5% K to ensure that the majority of trees are over 1.2%

35. Potassium Fertilization: • Average of 4 – 5 lb. K2O (3.3 – 4.2 lb. K) removed per ton of fruit • = 80 – 100 lb. K2O in 20 ton yield

36. Potassium Fertilizers: • Potassium can be tightly bound to clay particles so generally we apply high quantities in concentrated applications to overcome problem • Less of an issue in sandy soil or where active roots are very shallow • Drip or microsprinklers • Adding gypsum (CaSO4) can help K move deeper in soil

37. Potassium Fertilizers: • Potassium chloride (KCl) • Probably cheapest form per pound of K2O but risky due to Cl component • Should be applied after leaf drop in fall • Sulfate of potash (K2SO4) • More expensive than KCl but safer • Not soluble but can be applied through solutionizer • May be able to broadcast in sandy soil under microsprinkler

38. Potassium Fertilizers: • If banding sulfate of potash (K2SO4) in drip-irrigated orchard, drip hose must be placed over band

39. Potassium Fertilizers: • Potassium nitrate (KNO3) • Also supplies N which should be accounted for • Can be applied as foliar spray • Foliar KNO3 applied during stage III may be effective – high demand period • May require multiple sprays at 40 lb to correct deficiency • Potassium thiosulfate (KTS 0-0-25) • Efficiently applied with fertigation but more expensive

40. Zinc - Influences on Deficiency: • Soil pH – Zn availability decreases over pH 6.0 • Lime (calcium carbonate) ties up zinc. Magnesium carbonate is worse • Land leveling - zinc content decreases with soil depth. • High amounts of phosphorus (ties up zinc)

41. Zinc - Influences on Deficiency: • Organic matter and manure • Zinc is less available in soils with a high OM content. • Heavy manure - chicken manure is particularly bad • High levels of other metallic elements (copper, iron, manganese) can induce zinc deficiency • Cool, wet soils • Rootstock (nemaguard is bad)

42. Zinc Deficiency • Interveinal yellowing with mild zinc deficiency

43. Zinc Deficiency Very small, pale, pointy leaves in a rosette (very short space between leaves) with more severe zinc deficiency

44. Zinc Deficiency Extreme deficiency looks like glyphosate damage

45. UC Guidelines for Zinc in July-Sampled Leaves and Dormant Shoots 1Leaf samples are not reliable if orchard has been previously sprayed with zinc 2Recent experiments indicate that a threshold of 10 ppm zinc is more appropriate for July-sampled leaves

46. Foliar Applications of Zinc

47. Basic Chemicals Zn sulfate Zn oxide Zn carbonate Zn chloride Zn oxysulfate Zn nitrate Chelates & Complexes EDTA Lignosulfonate Amino acid Sugar Citric acid Fulvic acid, humic acid Zinc Materials

48. Zinc Materials Zinc Sulfate (35% Zn) • Inexpensive • Very soluble • Widely used • Considered to be effective • Can be phytotoxic

49. Zinc Materials Basic or Neutral Zinc • Cost = 2x Zn sulfate • Mostly insoluble • Widely used • Considered to be effective • Not phytotoxic • Can be mixed with oil

50. Zinc Materials Amino Acid Complexes • Expensive • Considered to be effective • Can be phytotoxic • 6 to 7% zinc