Pear Decline Research
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any other oat ever grown in this region. This means that windrowing will not gen- PEAR DECLINE erally be necessary for grain harvest. Both plant and seed are distinctive in appear- ance and the name choice. was mindful of RESEARCH both its history and appearance. Farmers cooperating in the testing program gen- erally have been enthusiastic about its po- W. H. GRIGGS * K. RYUGO * R. S. BETHELL K. URIU tential for hay or grain production. - The leaves are large and broad, stems large and strong, and panicles compact. Plants are generally similar to those of orchard was outstanding for its district and had a long record of consistently Ventura in height and maturity. They High summer temperatures appear to be mature with, and support, purple vetch an important contributing factor-in com- high yields. The trees in each orchard better than Kanota. Sierra has grey seeds, bination with psylla feeding-adding to were known to be on oriental rootstocks, shorter and wider than other California tree losses from pear decline. Thus far, and many had typical Pyrw pyrifoliu (serotina) root suckers for verification. varieties, with test weights only slightly none of the sprays, ground applications, Various stages of decline were found in higher than those of Indio. Crown and injections, or scoring treatments have had all three orchards at the beginning of the stem rust resistance of Sierra is genetic- any discernible effect on the progress of ally different from that in the other Cali- study (October 1960), but very few had pear decline. None of the treated or con- died in the Camino orchard. fornia oat varieties. This helps insure trol trees improved, a few apparently held against a general rtist epidemic on all our Trees were indexed for amount of their own, but most have deteriorated. varieties at the same time. Yellow dwarf terminal growth (1to 4, normal to none), virus resistance is not equal to that of amount of crop (1 to 4, heavy to poor), Kanota, our oat variety with the highest reddening of foliage (0 to 3, none to most degree of tolerance. HE DEVELOPMENT of pear decline leaves red), the presence of a brown line Sierra oats produced 30 per cent higher T was studied during 1960-61 in 627 on the cambial face of the bark at the grain yields than either Kanota, Ventura, trees in three orchards. The orchards graft or bud union, and date of collapse or California Red in state-wide California were in the Sacramento River district if tree died. tests, 1958-61 with local farm advisors near Ryde, and in the Sierra-Nevada foot- Treatments were applied to normal- cooperating. Hay yields, although not hills near Gold Hill and Camino. Before appearing trees as well as trees in various significantly better than these other vari- the onslaught of pear decline, each stages of decline. Some were given dilute eties, have been more consistent. The statewide tests have shown it to be PROGRESS OF PEAR DECLINE IN MATURE BARTLETT TREES ,ON PYRUS PYRlFOLlA (SEROTINA) adapted wherever oats generally are ROOTSTOCKS, 1960-61. adapted. Whereas the Curt variety is pri- Trees with brown line at grofi union Trees with no brawn line ai graft union marily a grain type, Sierra will be useful October 1960 October 1960 for forage or feed grain. Trees Num- Growth Leaf Trees With Leaf Trees Status. Cropb color= dead Nt'- yzz! Cropb brown color^ dad OAT VARIETY GRAIN YIELDS- ber Oct. line -oct. Of Oct. Oct. July Oa. Oct. 1961 Of Oct. Oct. July Oct. Oct. Oct. 1961 37 TESTS (1958-1961) trees 1960 1961 1961 1960 1961 (%) trees 1960 1961 1961 1961 1960 1961 (%) (%) Variety Yield os per cent of Konota Kanata ...................... 100 Elev. 19ft. .. 37 3.5 4.0 3.7 .. 1.6 48.6 142 1.8 2.0 2.2 35.9 . 0.4 13.4 Sierra ....................... 138 Gold Hill Curt ......................... 132 Elev. 1900ft. ..117 1.3 1.9 2.7 .. 0.9 26.5 36 1.3 1.6 2.3 50.0 .. 0.0 11.1 Ventura ...................... 108 Camino California Red ................ 99 Elev. 3000ft. ..185 1.9 3.1 3.4 1.8 2.0 1.1 110 1.8 2.1 2.7 36.4 0.4 0.6 0.0 Many useful characters in Sierra obvi- 1, normal growth; 2, reduced terminal growth; 3, two to four inches of terminal growth; 4, no terminal growth. ously came from its wild oat parent-in- I, 1, heavy crop; 2, good crop; 3, fair crop; 4, poor crop. dicating that perhaps the best hope for 0, green leaves; 1, same red leaves; 2, more red leaves; 3, most leaves red. the increased adaptation of oats to the arid regions of the world lies in other AVERAGE MAXIMUM TEMPERATURES AT STATIONS NEAR ORCHARDS UNDER STUDY. similar species crosses. June July August September Station Coit A. Suneson is Research Agrono- 1960 1961 1960 1961 1960 1961 1960 1961 mist, Crops Research Branch, A.R.S., Walnut Grove U. S. Department of Agriculture, Davis; (near Ryde orchard) ...... 90.5 90.2 93.4 94.0 92.2 91.3 87.5 85.4 4* 8* 9. 8' 2* 4" 0" 0' and Milton D. Miller is Extension Agron- Placerville (near Gold Hill orchard) .. 92.6 90.6 97.5 96.1 93.2 92.0 88.4 82.9 omist, University of California, Davis. 6' 10" 9' 8' 8' 2' o* 0' Camino- A progress report from Project 176 (near Camino orchard) .... 85.2 83.8 90.1 08.3 87.3 85.5 79.8 76.0 (U. S. Department of Agriculture and the O* 1' 1' O* 0' 0" 0' 0. Ftom climatological data of the U. S. Dept. of Commerce Weather Bureau and University of California, California Agricultural Experiment Sta- Department of Pomology. tion cooperating). Number of days temperature reached 100' F. or higher. CALIFORNIA AGRICULTURE, JUNE, 1962 9 nutrient splays of either phosphorus, ages (respectively 35.9,50.0, and 36.4 for phosphorus plus zinc, or phosphorus plus Ryde, Gold Hill, and Camino) were zinc plus iron during the dormant season rather consistent for all three locations. of 1960-61, and three times during the 1961 growing season. Others were Pear psyllu sprayed with zinc chelate (Zn EDTA, During November 1961, workers in 14.2 per cent zinc as metallic) at 5 pounds Washington presented evidence that pear in 100 gallons of water on October 17, decline is caused by a systemic toxin 1960 and again May 5, 1961. Others re- introduced by pear psylla (Psylla peri- ceived 1.5 or 3 pounds of iron chelate cola, Forester) feeding on the foliage. (Fe EDDHA, 6.0 per cent iron as metal- They found that the number of psylla per lic) broadcast from the trunks out about leaf was directly related to the amount of 8 feet and raked into the soil on October phloem injury, but that the toxin is SO 25, 1960, or March 24, 1961. Still others potent that relatively few psylla can cause were injected with 2,400 ml of iron great damage to pear trees on susceptible chelate at a concentration of 360 ppm rootstocks. They reasoned that psylla (iron as metallic) on October 19-20, alone may cause slow decline and that 1960. psylla coupled with adverse cultural en- PLUM ROOT vironmental conditions (e.g., hot dry Bark scoring Incompatibility periods) causes collapse or quick decline. During October 1960 and March 1961, If psylla are the cause of decline, the 362 trees were scored vertically to stimu- death rate and steady deterioration of An apparent mix-up within commercial late callus formation and possibly provide trees in the Ryde orchard substantiate the murces of the vegetatively-propagated an avenue for food and water movement conclusion that heavy populations are not through the area near the graft union, Marianna plum stocks with some other required for severe damage. Surveys by similar plum stocks has been revealed. where plugging of the sieve tubes had University entomologists showed that caused the girdling effect associated with Myrobalan plum seedlings, several vege- psylla populations are much lighter in tatively propagated myrobalan selections decline. Six to eight score wounds were Sacramento River orchards than around made through the bark down to the wood and two Marianna clones (2623 and 2624) Placerville and Camino. In the three have been commercially propagated for on each tree, with either a heavy knife or orchards under study, psylla control has a blight scraper. Short score wounds (4 roostocks of stone fruits for a number of been adequate to permit the production of years. Of these, only the two Marianna to 6 inches above and below the graft fruit suitable for fresh shipment. unions) were made on half of the trees, stocks can be used successfully for al- and long score wounds (from 4 to 6 inches Present study monds, and then only for certain varieties. below the unions to 4 to 6 feet above) on Marianna 2624 is the more important be- The present study points to high sum- cause of its resistance to oak root fungus the others. Two-thirds of the scored trees mer temperatures as an important adverse had their wounds filled with asphalt emul- and is the one most often propagated for condition that, in combination with almond rootstock. sion grafting compound, and a third were psylla feeding, can cause the death of untreated. trees. This is shown by the low death rate Ne Plus Ultra, Peerless Thus far, none of the sprays, ground of declining trees at Camino (3,000 feet ORDANOLO, and Texas (Mission) varieties will applications, injections, or scoring treat- elevation) compared with those at Gold J make a satisfactory graft combination ments have affected the progress of pear Hill (1,900 feet) and Ryde (19 feet).