1. Fruit Load and Fertilization Impacts on Late Season Foliar Decline : Fruit Load and Fertilization Impacts on Late Season Foliar Decline : Field Observations in the San Joaquin Valley Bob Hutmacher, UCCE Extension Agronomist – UC Shafter Steve Wright, Farm Advisor UCCE – Tulare & Kings Co. Dan Munk, Farm Advisor UCCE, Fresno Co. Bruce Roberts, CA State University, Fresno Mark Keeley, Staff RA, UCCE – UC Shafter REC Joe Fabry, Agronomist, Fabry Consulting, Fresno, CA Tome Martin-Duvall, Staff RA, UCCE – Madera Co. R. Michael Davis, Extension Plant Pathologist, UC Davis Gerardo Banuelos, Res. Asst. – UCCE – Tulare Co. Doug Munier (Farm Advisor, UCCE – Glenn Co.)

2. Merced Co. – 2007 Foliar “collapse” problems

3. Observations on fields with these symptoms / problems in the SJV of California Growth / meristems affected as early as early July in some fields more prevalent in sandy loam soils of Tulare and Kern Co. ‘s however, observed even in range of loam & clay loam soils in Fresno, Kings and Kern Co. in 2002, 2004, 2006, 2007 Many fields (particularly Pima fields) have been affected quite late in the growing season (late August through mid- September) some fields have very spotty, almost random appearance of symptoms, others much more uniform

4. 20-30% open boll, significant leaf loss & bronzing Varietal differences in symptom development Small plants with 3 bale boll load – collapse, not defoliated

5. - Worst Cases impacted duration of growth Yields reduced due to: fewer total nodes less fruiting branch development poor or arrested development of later bolls

6. Fruiting patterns – “good versus “affected” parts of field – Kings Co. - 2004 Example of fruiting patterns in high retention, sustained growth field versus declining vigor, affected field Estimated yld. (hand harvest) = 1780 lbs/ac Estimated yld (hand harvest) = 1300 lbs/ac fewer FP2, no FP3 bolls

7. Possible Causes of Early Decline, Foliar Collapse, Premature Senescence? 1.Environmental Factors a. Poor fertility of soils b. Prolonged periods of water stress c. High temperatures d. Nematodes e. Leaf Diseases 2. Physiological Factors a. High demand of nutrients and carbohydrates b. Reduced efficiency of roots nutrients uptake after bloom / possible varietal differences in root vs shoot and fruit growth

8. Additional symptoms associated with worst affected parts of fields Early developmental problems –Significant seedling disease injury –Major leaf loss or injury in early seedling stage (due to thrips, weather, etc.) Plant conditions correlated with more problems –Very high early fruit retention combined with water or temperature stresses that might limit roots or shoot growth and carbohydrate production more than fruit retention –Root growth limited by soil moisture, soil compaction

9. FRUIT Removal (Pima) – Timing of symptom development as affected by fruit removal – replicated, randomized plots - Kern Co. – 2002 Estimated yld. (hand harvest) = 1580 lbs/ac Estimated yld (hand harvest) = 1350 lbs/ac

10. FRUIT Removal (Pima) – Timing of symptom development as affected by fruit removal – replicated, randomized plots - Kern Co. – 2006 Estimated yld. (hand harvest) = 1440 lbs/ac Estimated yld (hand harvest) = 1170 lbs/ac

11. Pima – Timing of symptom development as affected by LEAF removal (alternate main stem & sympodial / nodes 3-11 from top) - Kern – 2006 Estimated yld. (hand harvest) = 1510 lbs/ac Estimated yld (hand harvest) = 1280 lbs/ac

12. Pima – Timing of symptom development as affected by LEAF removal (alternate main stem & sympodial / nodes 3-11 from top) - Kern – 2002 Estimated yld. (hand harvest) = 1630 lbs/ac Estimated yld (hand harvest) = 1190 lbs/ac

13. Correlations with other symptoms / measurements Plant nutrient status –low NO3, P, and K in late season normally –leaf and petiole K values generally low in all plants w/ symptoms, but these are low vigor plants by the times symptoms are obvious, severe Soil nutrient status –in fields sampled in late August and September with leaf and plant symptoms ranging from mild to severe, soil test K values have ranged from moderately deficient to adequate (few clear trends)

14. Exchangeable Soil K Exchangeable Soil K (mid-Aug. to early Sept. sampling dates) vs. Early Decline Symptoms (UCCE ) All fields Verticillium Vasc. Stain < 25% 73 fields sampled INDEX Early = clear 1 st symptoms at 15- 17 nodes Late = >17 nodes at 1 st symptoms Higher #’s indicate >% plts affected, more severe injury

15. Relative root and boll growth Number of nodes Roots Bolls First Bloom

16. Root Diameter/Lateral Index Root Diameter/Lateral Index (mid-Aug. to early Sept.) vs. Early Decline Symptoms (UCCE )– root diam. at 25 cm depth & # laterals>2.5mm, top 25 cm of tap root All fields Verticillium Vasc. Stain < 25% 26 fields sampled INDEX Higher #’s indicate >% plts affected, more severe injury

17. N & K fertilization (Pima – cv. DP340) – Yield and Symptom Development – Impacts of Fertilization – sandy loam soil - Kern Co. – 2006 Soil injected sol’n prior to irrigation * *

18. Verticillium or Nutrients? temperature conditions some of these years conducive to development of Vertic. more frequent or excessive irrigation can aggravate problem more affected fields seem to be in lighter soils, but not all root systems in many affected fields are somewhat stunted and secondary roots are limited or damaged, but not in all fields varietal differences in verticilium resistance and in streaking symptoms ? (not clear)

19. Fields evaluated in 2002 to 2007 had Verticillium infection rates (vascular staining) ranging from 0 to about 95% – so even late season was not the primary cause of collapse in many evaluated fields Fields evaluated in 2002 to 2007 had Verticillium infection rates (vascular staining) ranging from 0 to about 95% (but average was < 15%) – so even late season was not the primary cause of collapse in many evaluated fields

20. Impact of Foliar Damage on Yield Variable With Severity, Timing of Damage & Variety Sites with lower vigor plants, reduced # nodes Sites with higher vigor & boll load Gold=low symptom variety Blue=moderate Purple=high * don’t just choose variety with few symptoms

21. Suggested management practices to reduce impacts of this problem Evaluate soil K and perhaps plant N status (consider foliar K if soil test #’s low and plant tissue levels also low) –base decisions to some degree on plant vigor and fruit retention / potential boll load Reduce mgmt practices that result in restricted root zones (compaction, root pruning, other damage that limits ability to acquire nutrients) Identify fields with history of symptoms, test # of varieties with fewer symptoms to see if related to better yield performance, not just fewer symptoms Look at improved within-season fertilizer application trials and multiple variety plantings to evaluate potential to limit losses

23. Late-season, plants low in K, N, P, etc Soil K, N, P levels often in “sufficient” range leaf damage, stem & fruit development arrested in worst-affected fields fields affected late (much less impact) Tulare Co. – 2004

24. Feel a little like this on this subject? ---

25. Model of Potassium Stress (Juan Landivar, DPL / Texas A&M University) Soil Water, Available K Root Volume, Root Age Nematodes K Absorption, K Reserves Available K Temperature Age Turgor Roots, Stem, Leaves Squares, Bolls K Demand Potassium Stress Potential Growth

26. Germination Harvest Suggested Components of Fertility Program for reducing Early Decline problems 2827 1st Sq1 st Boll First Open Boll 55 40 Phase of Utilization P, K Deep Applied N, P, K (Sidedressed or Water run?) K, N, Micro Nutrients (foliar applications possible?) Phase of Absorption Starter fertilizer at Planting?

27. Leaf fungal damage seen, ozone damage? Weakened plants, limited or damaged root systems, multiple “stresses” (often little or mild Verticillium) Remedy with crop rotation to reduce pathogens & root damage, within-season nutrients, limit stress ?

28. Varietal differences in sensitivity Varietal differences in sensitivity foliar breakdown (Madera Co., late-August )