Pockets of grapevines weakened from feeding.

is difficult for a number of reasons. Phylloxera are often widely distrib­ uted throughout the root profile and can be found to great depths. chemistry, especially pH, may neutral­ ize an insecticide and reduce its effi­ cacy. Chemical movement through is uneven, depth of pen­ etration is often insufficient and cover­ age is limited by some methods of application. In addition, there are often environmental concerns about groundwater contamination. Even when there is initial high mortality of phylloxera, populations can rebound due their high reproductive rate, and there may be little improvement in Enzone does little to grapevine growth. In California, only carbofuran improve health of (Furadan) and sodium tetrathio­ carbonate (Enzone) are currently regis­ phyl loxera-infested vineyardstered for use against phylloxera in . The use of carbofuran in Napa, Sonoma and Mendocino coun­ Ed Weber o John De Benedictis 0 Rhonda Smith ties was banned in 1992 due to avian Jeffrey Granett mortality associated with its use. Enzone was granted full California registration in 1994. Enzone is a liquid formulation of Enzone was applied to phylloxera­ termed biotype B, has become a sig­ sodium tetrathiocarbonate. It is ap­ infested vineyards in four trials in nificant problem in Napa and Sonoma plied to soil with irrigation water, Napa and Sonoma counties from counties due to its ability to attack and where it rapidly breaks down to liber­ 1989 through 1994. Improvements kill grapevines growing on AxR#l ate predictable amounts of carbon in growth or were occasion­ . disulfide (CS 2), a general biocide . Car­ ally seen, but most occurred only North Coast vineyards are now be­ bon disulfide was widely used in Eu­ after the vines had been severely ing planted on other than ropean vineyards during the phyllox­ affected_by phylloxera and yields AxR#l that have adequate resistance era epidemic of the late 1800s, where it had plummeted. to phylloxera. Growers with existing was injected into soils. This technique AxR#l vineyards that are infested was dangerous because of the volatil­ with biotype B phylloxera are faced ity and explosiveness of CS 2, and it phylloxera, Daktulosphaira with declining yields and the need for was often phytotoxic to the vines. The vitifolia(Fitch), are aphidlike expensive replanting. Treatments that use of Enzone circumvents the danger that damage grapevines by feeding on would reduce phylloxera populations, of explosive volatility posed by direct roots. They can be destructive to vines slow the overall decline of the vine­ application of CS 2• that are own-rooted or grafted onto yard, and help maintain an economic Studies in our laboratory confirmed susceptible rootstocks. Rootstocks re­ level of production could allow them that the concentrations of CS 2 in va­ sistant to phylloxera have been used to delay replanting . pors or solution expected from Enzone for over 100 years to combat this . Historically the application of pesti­ applications are lethal to adult phyl­ In California's North Coast ­ cides to vineyard soils for control of loxera, larvae and eggs. From 1989 grape growing region (Napa, Sonoma, grape phylloxera has been ineffective. through 1994 we conducted several Lake and Mendocino counties), AxR#l While several chemicals have been field studies to evaluate the efficacy of has been the most popular rootstock. shown to kill phylloxera in laboratory Enzone in phylloxera-infested North Recently a new strain of phylloxera, studies, effective control in vineyards Coast vineyards.

CALIFORNIA AGRICULTURE, JULY-AUGUST 1996 19 TABLE 1. Enzone field trials: Locations and vineyard descriptions Field trials Irrigation Date Rowxvlne Pruning Our primary interest in the field Trial name Location Variety method planted spacing (ft) method studies was to determine if grapevine Napa 1992- 1994 Gameros Chardonnay Drip 1975 6 X 10 Canes & growth and yield would improve as a spurs result of Enzone applications. We Sonoma 1991-1994 Sonoma Valley Chardonnay Drip 1974 6 X 12 Canes & monitored phylloxera populations in spurs Napa 1990--1991 St. Helena Chardonnay Drip 1978 8 X 12 Cordon each trial, but we already knew from Napa 1989--1990 Rutherford Cabernet Furrow 1974 8 X 12 Canes& Sauvignon spurs laboratory work that CS2 produced from Enzone could kill phylloxera. Simply reducing phylloxera popula­ TABLE 2. Enzone fleld trials: Summary of treatments tions would not be considered a suc­ Number of cessful outcome unless there were also Trial name treatments Treatment descriptions positive effects on grapevine growth Napa 1992-1994 5 Water-only control and production. 5 gal/acre Enzone All experiments used randomized 5 gal/acre Enzone + 10 gal/acre Enzone complete block designs in vineyards 1O gal/acre Enzone + fertilizer on AxR#l rootstock infested with bio­ Sonoma 1991-1994 2 Water -only control type B phylloxera. Enzone was applied 7 gal/acre Enzone (15 gal/acre in 1991) with drip irrigation in three trials and with furrow irrigation in one trial. Use Napa 1990-1991 2 Water -only control 15 gal/acre Enzone of a spray-blade injector is discussed later in this article. Untreated controls Napa 1989--1990 2 Water-only control were irrigated at the same rates as Enzone @ 300 ppm ai treated vines in all trials. Table 1 de­ scribes the vineyards used for the field in May 1993 and following in for sugar (degrees ), titratable trials. October 1992 and 1993. In each single­ acidity and pH. At harvest, the 12 data At the onset of these trials there row replicate, 21 vines were selected vines in each replicate with undis­ was no recommended strategy for us­ for data collection. Nine were used for turbed roots were individually har­ ing Enzone in vineyards. Treatments root sampling and phylloxera rating; vested. Crop weight and cluster num­ were selected with input from the 12 were used to evaluate crop yields ber per vine were measured and manufacturer's research staff and were and vine growth. The same data vines average cluster weights were calcu­ intended to evaluate efficacy and to were evaluated each year. lated. Numbers of berries per cluster develop an effective Enzone applica­ Phylloxera populations were rated were calculated from average cluster tion strategy for North Coast vine­ by digging roots from soil underneath weight and berry weight data. During yards. As a result, treatments varied the drip emitters and examining them the dormant season, pruning weights among the field trials (table 2). for the presence of phylloxera. Vines of 1-year-old wood were measured as Napa 1992-1994. In 1991 the vine­ received a rating based on the highest an indicator of vine growth. Treatment yard showed early signs of decline population found among the root means were subjected to analysis of due to biotype B phylloxera. A trial pieces examined. Ratings were made variance. with five replications of five treat­ on 3 vines per replicate on each sam­ Sonoma 1991-1994. The trial was ments was initiated in 1992. Enzone pling date. Vines were rated on the conducted in 20 rows, each containing was applied through the drip system numbers of phylloxera found, as fol­ 80 vines. Enzone or a water-only con­ at rates of 5 and 10 gallons per acre lows: trol treatment, replicated 10 times, was (gal/ ac). The other treatments were 0 - No phylloxera found. applied to entire rows through the Enzone at these rates with the addition 1 - Phylloxera only on rootlets, or drip system. There were two 1-gph of potassium nitrate applied through one or two individuals on older (than emitters per vine. Phylloxera were the drip system, and a water-only 1 year) roots. present throughout the trial area when it control. Fertilizer additions made in 2 - Individual phylloxera scattered was established in 1991, although only 1992 and 1993 totaled approximately among older roots, or one or two colo­ half of the vines were symptomatic. 5 pounds per acre (lb/ ac) N and nies on older roots. Treatments were applied four or 15 lb/ ac K20 per season. Treatments 3 - Several colonies established on five times per year. In 1991, 15 gal/ ac were made to entire rows of grape­ older roots. of Enzone were applied on each appli­ vines. There were two 0.5-gallon-per­ 4 - Large populations of phylloxera cation date for a total of 75 gal/ ac. In hour (gph) emitters per vine. present on older roots. the following years, application rates In each of the three years, treat­ Berry samples were collected from were 7 gal/ ac and the total amount ments were made in June, July and each replicate prior to harvest and of Enzone applied ranged from 28 to August, with additional applications weighed. Extracted juice was analyzed 35 gal/ ac.

20 CALIFORNIA AGRICULTURE, VOLUME 50, NUMBER 4 We selected five vines per row as data vines, from which yield compo­ nents and pruning weights were indi­ vidually measured throughout the du­ ration of the trial. Opposite-cluster bloomtime petioles and preharvest berry samples were collected by repli­ cate. Crop yields from entire indi­ Above left, equipment for Injecting Enzone into Individual drip lines. Above, Enzone being vidual rows (replicates) were also applied with furrow irrigation. taken. Roots were collected from each replicate on two or three dates each year, and phylloxera populations were rows 102 to 104 vines long. Berms of licate and analyzed for berry weight, assessed by a private consultant. soil were raised between every vine degrees Brix, titratable acidity and pH. Napa 1990-1991. The vineyard row to contain the applied irrigation At harvest, all the fruit from each two­ was planted in 1978 and irrigated with water. An untreated buffer zone two row replicate was harvested by a com­ overhead sprinklers until 1990, at vine rows wide was used between mercial picking crew, placed in gondo­ which time a drip irrigation system Enzone and control treatments. Well las, and weighed. was installed specifically for the appli­ water was delivered to the appropriate Field trial results cation of Enzone. There were two 1-gph areas via 12 -inch surface irrigation emitters per vine. Twelve replications pipes . Enzone was injected into the ir­ Napa 1992-1994. There were no of two treatments were used for the rigation waters to reach a final concen­ significant differences (p > 0.05) in trial: Enzone applied through the drip tration of 300 ppm ai. fruit production in any year between system at 15 gal/ ac and a water-only Treatments were made in Novem­ the individual treatments, and few sig­ control. Treatments were applied to ber 1989 and May 1990 to coincide nificant differences in phylloxera rat ­ entire rows of vines. Three applica­ with fall and spring root flushes. No ings or fruit composition (data not tions were made in 1990 (May, August additional treatments were made be­ shown). However, when orthogonal and October) and four in 1991 (June, cause the vineyard was removed fol­ contrasts were used to compare all July, August and November). lowing harvest in 1990 . Enzone treatments to the water-only In each single-row replicate, 14 data Phylloxera ratings, as previously control, some differences were found vines were selected for data collection. described, were made at every tenth (tables 3 and 4). Six were used for phylloxera ratings vine in one row of each replicate be­ Phylloxera populations were re­ and 8 were used to evaluate crop fore and 3 to 4 weeks after each duced by Enzone applications (table 3) . yields and vine growth. The same data Enzone application, and again 1 week That the reduction was not seen at vines were used each year. Phylloxera after harvest in 1990. A vigor rating each sampling date is probably a limi­ ratings and growth and yield mea­ based on the appearance of the vines tation of our sampling method in a surements were made as described was made in October 1989, prior to the drip-irrigated vineyard (some root above for the Napa 1992-1994 trial. first application, and again in Septem­ pieces may have come from the mar­ Napa 1989-1990. Our first field ber 1990, a week prior to harvest. All gin or outside of the wetted area and trial of Enzone used furrow irrigation vines in one row per replicate were thus not been fully exposed to lethal and included eight replications com­ rated on a scale from 1 to 5 , with 5 rep­ CS2 concentrations) and a function of paring Enzone applications to control resenting vines with strong growth the lower phylloxera populations in treatments of water only . A pretreat­ and healthy appearance and 1 repre­ the second and third years of the trial. ment survey of roots revealed phyllox­ senting vines that were severely It is interesting to note that the era throughout most of trial area, even stunted from phylloxera damage. phylloxera ratings in the untreated though most vines appeared healthy. Prior to harvest in 1990, berry control vines were much lower in 1993 Replicates consisted of two adjacent samples were collected from each rep- and 1994 than in 1992 (table 3). This is

CALIFORNIA AGRICULTURE, JULY-AUGUST 1996 21 While Enzone applications led to TABLE 3. Napa 1992-1994: Effect of drip appllcatlons of Enzone on phylloxera population ratings In small yield improvements in 1993 and a Chardonnay/AxR#1 vineyard 1994, production in these years was 1992 1993 1994 considerably lower than in 1991 and 1992 (fig. 2). Treatment Jun• Jul Aug Sep May Jun Jul Oct May Jun Jul Oct Nutrient levels in petioles collected Control 2.33t 3.20 2.33 3.20 0.87 1.07 1.07 1.87 0.83 0.53 1.07 1.87 in 1994 (data not shown) indicated Enzone 2.n 1.85 1.52 2.23 0.47 0.63 1.13 1.10 0.73 0.47 0.57 1.85 that Enzone-treated vines had signifi­ prob. 0.231 0.003 0.031 0.028 0.046 0.001 0.731 0.013 0.505 0.671 0.004 0.940 cantly higher levels of potassium and ·Prior to first Enzone applications . zinc, and lower levels of calcium and tSee text for description of phylloxera rating scale Q-4 . magnesium, than did control vines (p < 0.05), while petiole nitrate-nitro­ TABLE 4. Napa 1992-1994: Effect of drip appllcatlons of Enzone on crop weight, cluster number gen levels did not differ. and pruning weights In a phylloxera-lnfested Chardonnay/AxR#1 vineyard Enzone applications significantly

Year Treatment Lb/vine• Clusters/vine Pruning weight reduced the number of phylloxera or (tons/acre) eggs found on roots on at least one sample date each year (data not lb/vine shown). 1992 Control 13.1 (4.8) 31.5 1.36 Napa 1990-1991. Reductions in Enzone 13.3 (4.8) 33.1 1.43 phylloxera populations were observed prob. 0.829 0 .444 0.629 on some sampling dates; however, 1993 Control 5.01 (1.8) 12.1 0.78 there were no significant differences in Enzone 6.09 (2.2) 14.1 0.97 prob. 0.061 0.079 0.005 any vine growth or yield parameters measured in either year of the study 1994 Control 5.17 (1.8) 11.1 0.89 (data not shown). The trial was discon­ Enzone 6.97 (2.5) 13.7 1.14 prob. 0.059 0.035 0.006 tinued after the second year and the vineyard was subsequently replanted. •crop weights collected from 300 data vines. Tons/acre based on 726 vines/acre . The vines were 12 years old when the trial began. Previously, the vine­ likely due to the weakened condition Sonoma 1991-1994. There were no yard had been irrigated with overhead of the vines, as evidenced by their re­ significant treatment effects on any of sprinklers and the vines had devel­ duced growth and yield. When evalu­ the parameters measured in the first oped a deep, well-distributed root sys­ ating phylloxera, we have repeatedly 2 years of the trial (p > 0.05, data not tem. Because there was no history of seen that weakened vines do not sup­ shown). In 1993 and 1994, Enzone­ drip irrigation, there was no concen­ port large phylloxera populations, treated vines had significantly higher tration of roots below the emitters, as whereas nearby vines that appear yields, with larger cluster and berry would typically occur. As a result, our healthy can support large populations. weights, than did the control vines Enzone applications were likely affect­ Enzone applications led to yields (table 5). There were no significant dif­ ing a smaller percentage of the overall that were nearly significantly greater ferences in clusters per vine, berries root system than would occur in vine­ than control vines (p = 0.06) in the sec­ per cluster, juice analyses or pruning yards that have been continuously ond and third years of the trial (table 4), weights in any year. drip irrigated. due primarily to higher cluster counts. However, yield throughout the block, including the Enzone treatments, 4.4 5 4.5 plummeted from an average of 4.8 D Enzone D Enzone • Control u4 .o • Control tons per acre in 1992 to just over 2 tons CJ 4 -!!! 3.5 -!!!- per acre in 1993 and 1994 (fig. 1). Ill ~ 3.0 C 3 2.4 There was a similar reduction in 0 2.53 £ 2.5 :; 2.0 vine growth after 1992, as indicated by "O- 2 - ai 1.5 pruning weights (table 4). Enzone­ ai 1 > 1.0 treated vines had higher pruning > 0.5 weights than control vines in 1993 and 0 0 1992 1993 1994 1991 1992 1993 1994 1994, but both treated and untreated vines had considerably lower pruning Fig. 1. Yield comparisons of Enzone­ Fig. 2. Yield comparisons of Enzone­ weights than they had in 1992. There treated and control (water-only) vines, treated and control (water-only) vines, were no significant differences in clus­ Napa 1992-1994 trial. Data collected from Sonoma 1991-1994 trial. Data collected ter weights, berry weights, berries per 300 selected data vines; tons/acre based from all treated and control vines; tons/ on 726 vines/acre. acre based on 605 vines/acre. cluster or juice analyses in any year *Yields were significantly different (data not shown). (p< 0.05) in 1993 and 1994.

22 CALIFORNIA AGRICULTURE, VOLUME 50, NUMBER 4 two applications, it was clear that ad­ ditional treatments would be required TABLE 5. Sonoma 1991-1994: Effect of drip applications of Enzone on crop weight and selected for adequate control of phylloxera. yield components In a phylloxera-lnfested Chardonnay/AxR#1 vineyard Unfortunately, nearly all vineyards in Year• Treatment Lb/vine Cluster weight Berry weight (tons/acre)t the North Coast region have uneven terrain or limited water availability, lb gm which prevents this type of irrigation. 1993 Control 6.4 (1.9) 0.27 0.81 Enzone 8.2 (2.5) 0.30 0.89 Additionally, applying large amounts Probability 0.001 0.006 0.001 of water during the summer would of­ ten be detrimental to fruit and wine 1994 Control 6.2 (1.9) 0.27 1.05 Enzone 9.2 (2.8) 0.33 1.17 quality. Probability 0.001 0.006 0.018 Many of these vineyards, however,

'Enzone applied 1991-1994 . do have overhead sprinklers. In an at­ tCrop weights collected from 100 data vines . Tons/acre based on 605 vines/acre. tempt to treat a higher percentage of the root system than is possible with drip irrigation, we experimented with Napa 1989-1990. The first applica­ come economically unproductive. Enzone applications through a spray tion of Enzone in November 1989 re­ Vines often remain in this weakened blade, followed by sprinkler irrigation duced the phylloxera population from condition for several years before fi­ to move the Enzone through the soil a rating of 3.0 to 0.6 (p < 0.001). The nally succumbing, during which time profile. However, this trial was discon­ second Enzone application had little phylloxera populations are relatively tinued after the first year as yields apparent effect; however, the popula­ low. were reduced by 22% where the spray tion was already at a very low level In our trials, Enzone applications blade was used (data not shown). We prior to this application. By October through the drip system were unable attributed this crop loss to physical 1990 the phylloxera populations had to prevent the marked decline in vine damage to the root system caused by greatly increased, achieving a rating of productivity. In some trials, Enzone­ the spray blade itself. 2.7 even within the Enzone treatments. treated vines did produce more than Clearly, additional applications during the controls, but their yield was still Summary the summer of 1990 would have been quite low. The increased production When applied to vineyard soils, necessary to keep the population in likely justified the cost of applying Enzone kills phylloxera but may have check. Enzone, but it is doubtful that the eco­ little or no effect on vine growth and Despite the reestablishment of a nomic life of the vines was extended. productivity. In order to keep phyllox­ large phylloxera population during Yields dropped to a point where many era populations at a relatively low the summer, vines treated with growers would have pulled out the level, multiple applications are re­ Enzone had significantly higher yields vines whether they had been treated quired. Furrow applications are likely than the control vines (13.5 versus 12.2 with Enzone or not. to be more effective than drip applica­ lb/vine; p = 0.017) due in part to Drip applications by their nature tions, due to the increased coverage of greater berry weight (1.16 versus 1.09 treat a limited volume of soil and the root system. To maximize the ef­ gm; p > 0.009). reach only a fraction of the root sys­ fectiveness of Enzone with drip irriga­ Enzone-treated vines had higher tem. In both the Napa 1992-1994 and tion, the vineyard should have a his­ vigor ratings in September 1990 than Sonoma 1991-1994 trials, the vines tory of drip irrigation, and root did the controls (3.7 versus 3.4; were established with drip irrigation coverage should be maximized by the p = 0.041). However, vigor ratings of and likely had roots concentrated be­ number and size (gph) of emitters both treated and control vines were low the emitters. The Sonoma 1991- used per vine. lower than those made in October 1994 trial showed a small positive In our trials, Enzone-treated vines 1989 (4.5). This suggests that while all yield response to Enzone, and the were still severely affected by phyllox­ of the vines were damaged by phyllox­ Napa 1992-1994 trial suggested one era, and yields were greatly reduced. era, Enzone applications slowed their (p < 0.06). However, the yield im­ In some cases, Enzone applications led rate of decline. provements came only after 2 to 3 to higher yields after 2 or 3 years, but years, by which time productivity had these yields were well below previous Discussion been greatly reduced. There was no production levels. Phylloxera populations typically in­ apparent response to Enzone in the crease in size for 1 to 3 years, during Napa 1990-1991 trial, where the vine­ E. Weberis ViticultureFarm Advisor, UC which time vine growth and produc­ yard had no history of drip irrigation. CooperativeExtension, Napa County; tion are relatively unaffected. An eco­ Application of Enzone with furrow ]. De Benedictisis Staff ResearchAssociate nomic threshold for phylloxera popu­ irrigation greatly increases the per­ and]. Granettis Professor,Department of lations is unknown; however, at a centage of the root system that can be Entomology,UC Davis;and R. Smith is certain point growth and yield are treated. While we saw a good re­ ViticultureFarm Advisor, UC Cooperative markedly reduced and the vines be- sponse with furrow irrigation with just Extension,Sonoma County.

CALIFORNIA AGRICULTURE, JULY-AUGUST 1996 23