Milkweed Establishment in California's Central Valley

September 2020 FINAL STUDY REPORT Lockeford Plant Materials Center Lockeford, California

Milkweed Establishment in California’s Central Valley: II. Comparison of Asclepias eriocarpa, Asclepias fascicularis, and Asclepias speciosa by Seed Valerie Bullard, Jessa Kay Cruz, Margaret Smither-Kopperl

ABSTRACT Populations of milkweed species in California have declined in recent years resulting in fewer breeding sites for monarch butterflies. Milkweed species are frequently included in pollinator mixes, although poor establishment of milkweed species were observed at the Lockeford Plant Materials Center and in plantings by the Xerces Society. The objective of this replicated study was to compare establishment of three species of milkweed: woollypod milkweed(Asclepias eriocarpa); narrow leaf milkweed (Asclepias fascicularis), and showy milkweed (Asclepias speciosa), from seed in a randomized complete block design with four replications. The site at the Lockeford Plant Materials Center was solarized in the summer of 2017 and plantings made into a firm seed bed with a no-till drill at 15 seeds per square foot after a rainfall event. Plants were irrigated during the first year of the trial and frequent weeding was required. Evaluations were made during 2018 and 2019 for germination and survival, plant height, disease resistance and insect resistance. Woollypod and narrow leaf milkweed were first to emerge in early April 2018, and showy milkweed emerged in early May. By the end of the 2018 growing season, narrow leaf milkweed had a significantly higher survival rate (moderate to good survival), than showy milkweed (fair survival). In 2019, showy milkweed emerged in mid-April, while woollypod and narrow leaf milkweeds emerged in late April 2019. Overall, showy milkweed had higher survival rates, lower insect and disease damage and was significantly taller in height than the other two species.

INTRODUCTION. Milkweed species are critically important for survival of monarch butterflies (Danaus plexippus) as they are the primary larval host for the caterpillars. Western populations of monarch butterflies overwinter on the California Coast. The butterflies set out each spring on their annual migration to other western states and seek populations of milkweed plants on which to lay their eggs. There are numerous, overlapping generations of monarch butterflies each year as they complete their migration throughout California, into Nevada and Idaho, returning to their overwintering sites along the California Coast late in the fall. Xerces volunteer Thanksgiving counts of overwintering western monarch butterfly populations in groves on the California coast have declined precipitously in recent years (Pelton, 2017; Xerces Society, 2020). The 2018 Xerces Thanksgiving count was less than 30,000 butterflies, a 99% drop since 1997. This large drop causes concern of a quasi-extinction event for the western monarch (Pelton et al. 2019).

A major factor contributing to these declines is the loss of milkweed plants across the western monarch’s breeding range. A year-round population model showed that losses to breeding sites

Margaret Smither-Kopperl, Manager; Valerie Bullard, Agronomist, Lockeford Plant Materials Center, 21001 N. Elliott Rd., Lockeford, CA 95237. Jessa Kay Cruz, Senior Pollinator Conservation Specialist Xerces Society, [email protected]. 2 had four times the impact as the loss of overwintering sites (Flockhart, et al. 2015; Pelton et al. 2019). California’s Central Valley has recently been suggested as habitat of historic importance for milkweed populations, necessary for egg laying and successful survival of monarch populations (Espeset et al., 2016). The Central Valley is one of the most intensively farmed areas in the world resulting in major loss of native habitat. Extensive use of herbicides and cultivation is linked with loss of milkweed in fields and field borders (Pleasants and Oberhauser, 2012). This study focused on establishment of three milkweed species, woollypod, narrow leaf and showy milkweed, which are widely distributed and commercially available.

Woollypod milkweed is distributed through the Coast Ranges and the Sierra Foothills of California (Calflora, 2017). It is a perennial with rarely branching, densely hairy stems up to 3 feet tall (Borders, 2012; Rosatti and Hoffman, 2017). The dark green leaves are opposite and oblong to oval and covered above with dense hairs and prominent yellow mid‐veins. The umbels emerge from the uppermost nodes, the flowers moderately large and greenish to yellowish cream, while flushed with rose. Woollypod milkweed produces upright pods that are densely hairy, tapering to a tip, these from 1 to 3.5 inches in length (Rosatti and Hoffman, 2017).

Narrow leaf milkweed is distributed throughout California, apart from the desert regions (Calflora, 2017). They are erect perennials with smooth stems, with both axillary and terminal umbels with many greenish white and purple tinged flowers, 2 to 3 feet in height (Borders, 2012; Rosatti and Hoffman, 2017). The persistent leaves are whorled with 3 to 5 leaves at each node, each of these are narrowly linear with a tapered base, these are less than one inch wide but usually smaller and 4.5 inches long, smooth on top. The umbels are rounded on top and made up of numerous flowers with grayish pink to nearly white but greenish corolla. The upright pod is smooth and 2 to 5 inches long and less than a half inch wide (Rosatti and Hoffman, 2017).

Showy milkweed is distributed in the Coast Ranges and Sierra Foothills of California mainly north of Merced and the San Francisco Bay (Calflora, 2017). The plant is sturdy, single or multi- stemmed, up to 4 feet tall, with large opposite leaves that terminate in several umbels near the top of the stem with large pink to purplish flowers (Borders, 2012; Rosatti and Hoffman, 2017; Stevens, 2010). The umbels are between 1.5 and 3 inches across with flowers about a half‐inch across that have elongate hoods. The stems have opposite spade‐shaped leaves that are fuzzy on both sides with rather woolly hairs below. The pods are upright, 4 to 5 inches long and covered with hairs and some have warty projections (Rosatti and Hoffman, 2017).

The Xerces Society recommends milkweed species in hedgerow and pollinator plantings (Borders and Lee-Mader, 2014). Observations by the Xerces Society in pollinator plantings in California and at the Lockeford PMC indicate that milkweed establishment, as part of a pollinator mix, is frequently unsuccessful. Likewise, milkweed transplants are less likely to establish than other pollinator plants. The reason for the lack of success of milkweed establishment is not clear as guidelines used successfully for other species are followed (Borders and Lee-Mader, 2014).

The objective of this study is to compare the establishment of three different milkweed species, woollypod, narrow leaf, and showy milkweed, after fall seeding . The results reported here are part of a larger milkweed establishment study at the CAPMC. The additional reports are: Milkweed Establishment in California’s Central Valley: I. Showy Milkweed, Asclepias speciosa 3 by Seed, Rhizome and Transplants, and Milkweed Establishment in California’s Central Valley: III. Comparison of Milkweed Species Asclepias eriocarpa, A. fascicularis, and A. speciosa by Transplants.

MATERIALS AND METHODS The milkweed establishment trial was conducted over two years (2017-2019) at the Lockeford Plant Materials Center (CAPMC). The CAPMC is located on the eastern side of the San Joaquin Valley in central California and sits on a historical flood plain on the west bank of the Mokelumne River. The soil series is a Columbia fine sandy loam on 0 to 2 percent slopes. It is a very deep, well-drained soil with pH ranging from moderately acid to slightly alkaline. The mean annual maximum temperature in this area is 73.6°F and minimum temperature is 46°F (WRCC, 2018). The mean annual precipitation is 17.24 inches, mainly occurring between the months of December and March (WRCC, 2018). Precipitation totals were just below average (16.8 inches) between September 1, 2017 and August 1, 2018 and were above average (24 inches) between September 1, 2018 and August 1, 2019 shown in Figure 1 (WWG, 2019).

7 120.0

6 100.0 F) °

5 80.0

4 60.0 3

40.0 2 Monthly Total Precipitation (in) 20.0 1 ( & Min Max Temp Monthly Mean

0 0.0 Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul

Total Precip 2018-2019 Total Precip 2017-2018 Mean Monthly Precip Avg Max Temp 2018-2019 Avg Max Temp 2017-2018 Mean Monthly Max Temp Avg Min Temp 2018-2019 Avg Min Temp 2017-2018 Mean Monthly Min Temp

Figure 1. Mean minimum and maximum temperatures in the 2017/2018 and 2018/2019 growing seasons generally followed annual averages. Total precipitation was just below average in 2017/2018 and above average in 2018/2019. Monthly weather data from September through August was provided from Western Weather Group Lockeford Weather Station located directly across the river from the CAPMC. Average weather summaries from 1893-2015 for the Lodi area were provided from Western Regional Climate Center.

Site Preparation Site preparation began in June 2017. Weeds and the remaining residue from the previous fall planted cover crop were disked. The area was chisel plowed and cultipacked to prepare a firm seed bed and smooth solarization surface. Sprinkler handlines were laid to provide adequate soil 4 moisture. The UV-treated, 4 mm plastic was installed in June for maximum solar incidence for weed control. The solarization treatment effectiveness was marginal as nutsedge (Cyperus spp.) was growing under the plastic. Nutsedge was dug up and removed prior to planting and additional harrowing and cultipacking was also required to control the germinating weeds prior to planting the milkweed trial. Recycled solarization plastic was used for this project resulting in patching together multiple small pieces of plastic which may have decreased the efficacy of this usually effective site preparation method.

Planting Materials Milkweed seed was provided by Hedgerow Farms (Winters, CA). Seed was available for all three milkweed species evaluated: A. eriocarpa, woollypod milkweed, A. fascicularis, narrow leaf milkweed and A. speciosa, showy milkweed.

Experimental Design The experimental design was a Randomized Complete Block Design with four replications. The blocks were oriented to remove variation due to a slight moisture and soil texture gradient.

Seed Planting Seeding occurred on November 6, 2017. No pre-irrigation of the plots occurred as soil was moist from a previous rainfall. A Great Plains (Salina, KS) no-till drill was used to plant the seed 1 into 5 x 20 feet plots at a seeding rate of 15 live seeds per square foot to /2-inch depth (Figure 2).

Irrigation Drip irrigation was applied for establishment during the first year of the milkweed study. Each plot had 4 lines of drip tape spaced evenly in the plot with an irrigation set run in March, May, June and July.

Weed Control Weeds were controlled through cultivation during the first year, which was mainly hand hoeing. This technique was extremely time consuming. The emerging seedlings were small and fragile in early spring and looked fairly similar to Conyza bonariensis (hairy fleabane) and C. canadensis (horseweed) which are two very common wind dispersed weeds in the Central Valley. Some straw much was also used in the spring of 2018 after emergence, A pre-emergent herbicide was applied in winter 2019 while the milkweeds were dormant.

Evaluations Several evaluations were collected during the 2018 and 2019 growing seasons following national Plant Materials Program protocol, including: germination/survival, plant height, disease resistance and insect resistance.

Germination/survival was defined as germination percentage and survival percentage. Evaluations were conducted every 7 days during the initial emergence/transplant period and then every 14 days over the summer. Germination/survival was rated on a 0 - 4 scale, where 0 = poor (<25% germination/survival), 1 = fair (30 – 45% germination/survival), 2 = moderate (50 - 65% germination/survival), 3 = good (70 - 80% germination/survival), and 4 = excellent (90 - 100% germination/survival). Plant height was defined as the average height of lush canopy growth. Plant height was measured in inches from the base of the plant to the top of the inflorescence 5

every 30 days from three randomly selected plants within each plot. Disease and insect resistance were visual estimates of foliar diseases and insect damage. Plots were rated every 14 days on a 0 - 5 scale, where 0 = no damage and 5 = severe damage.

Statistical Analysis Statistical analysis was completed on the evaluations collected from the 2018 and 2019 growing seasons using Statistix 10 (Analytical Software, Tallahassee, FL). Ordinal data (germination/survival and disease and insect resistance) was analyzed using Kruskal-Wallis one- way analysis of variance (AOV) and Dunn's All-Pairwise Comparisons Test to separate means at the 5% level. Analysis was done on quantitative plant measurements (plant height) using the analysis of variance (AOV) procedure for a randomized complete block design (RCBD) along with Tukey’s 1 Degree of Freedom test for non-additivity. Significant means were separated with Tukey’s Honestly Significant Difference (HSD) All-Pairwise Comparisons Test at the 5% level.

Figure 2. Preparing to plant milkweed seed with a Great Plains no-till drill.

RESULTS AND DISCUSSION Three fall seeded milkweed species were evaluated throughout the 2018 and 2019 growing seasons for germination and survival, height, and disease and insect resistance. Germination evaluations began in late March of 2018. Woollypod milkweed and narrow leaf milkweed emerged in early April 2018 (Figure 3), significantly earlier than showy milkweed (Table 1). Showy milkweed did not emerge until early May 2018. At the end of the 2018 growing season, narrow leaf milkweed had a significantly higher survival rate (moderate to good survival), than showy milkweed (fair survival).

In 2019, showy milkweed was the first milkweed species to emerge in mid-April (Table 2). The other milkweed species did not emerge until late April. There was no significant difference in emergence between the species. In mid-May, all three milkweed species had fair emergence ratings. Showy milkweed had significantly higher survival rates (fair survival) than narrow leaf milkweed and woollypod milkweed (poor survival) in August 2019 due to high pest pressure.

In the 2018 growing season, narrow leaf milkweed was significantly taller than the other milkweeds (Table 3 and Figure 4). In mid-September, narrow leaf milkweed mean height was 26.8 inches, while the mean showy milkweed height was 15.7 inches and woollypod milkweed was 10.4 inches. In 2019, showy milkweed was significantly taller than the other two milkweed 6

species with a mean height of 51.2 inches (Table 4 and Figure 5). In April 2019, woollypod milkweed was significantly shorter than the other species with a mean height of 5.7 inches. By August, woollypod milkweed had a mean height of 26.3 inches, surpassing narrow leaf milkweed with a mean height of 15.2 inches.

During the 2018 growing season, disease and insect damage were not detected until mid-August (Table 5). The plants were infested with oleander aphids. Disease, in the form of black sooty mold, appeared due to the large quantities of sticky honeydew produced by the aphids. There were no significant differences in disease or insect resistance between species during the 2018 growing season. Showy milkweed had slight disease and slight to moderate insect damage, while narrow leaf milkweed and woollypod milkweed had moderate disease and insect damage in September 2018.

In 2019, disease and insect pressure were detected earlier and with higher severity. Insect damage was detected on all species in late June. From June to mid-July showy milkweed had significantly lower insect damage (slight) than the other two milkweed species (slight to moderate damage) (Table 6). From late July through September 2019, all three milkweed species showed moderate insect damage from the oleander aphid. Disease damage also appeared on all species in late June 2019. Showy milkweed had significantly lower disease damage (slight to moderate) than narrow leaf milkweed (moderate to severe) from June through August 2019. In August 2019, severe disease damage destroyed the aboveground growth of narrow leaf milkweed. However, new shoots were produced from the base of the plants. Disease damage remained slight to moderate on the new shoots through September. From August to September 2019, showy milkweed exhibited moderate disease damage, while woollypod milkweed had severe disease damage.

Results of this study indicate that seeding narrow leaf milkweed is an effective method of establishment. However, it has lower pest resistance than the other species evaluated. Wollypod milkweed had similar pest resistance to narrow leaf milkweed, with fair germination from seed, but severe disease damage caused poor survival during the second year. Conversely, successfully seeding showy milkweed requires intensive management during the first year to ensure good establishment due to a slower growth rate than the other species. Once established, showy milkweed exhibited higher survival rates and more insect and disease resistance than the other milkweed species in this trial. Showy milkweed plants were also taller the second year, which could indicate an ability to compete with weeds early in the growing season. Establishment and survival rates of all three species can be improved with supplemental irrigation and intensive weed management during the first year. Scouting for insect and disease presence early in the growing season is highly recommended. Any control measures used must be non-toxic to monarch butterflies and caterpillars, as well as taking into consideration effects on the many other beneficial insects foraging and sheltering in monarch habitat.

Figure 3. Woollypod milkweed seedlings germinating in April 2018.

Table 1. Germination and survival evaluations of three milkweed species at the Lockeford Plant Materials Center, CA 2018. Fall Seeded Milkweed - 2018 Germination and Survival Evaluations ꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷGermination/ Survival¥ꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷ Planting Type Planting Date 4/5/2018 4/11/2018 5/2/2018 5/10/2018 6/6/2018 6/11/2018 7/5/2018 8/1/2018 8/30/2018 9/12/2018 Asclepias eriocarpa 11/6/2017 0.8 ab 1.0 a 1.0 ab 1.0 ab 0.8 ab 0.8 ab 1.8 ab 1.8 ab 2.0 ab 2.0 ab Asclepias fascicularis 11/6/2017 1.0 a 1.0 a 1.3 a 1.3 a 2.3 a 2.5 a 2.5 a 2.0 a 2.5 a 2.5 a Asclepias speciosa 11/6/2017 0.0 b 0.0 b 0.3 b 0.3 b 0.3 b 0.3 b 1.0 b 1.0 b 1.0 b 1.0 b Mean 0.6 0.7 0.8 0.8 1.1 1.2 1.8 1.6 1.8 1.8 # SD 0.5 0.5 0.6 0.6 1.0 1.1 0.8 0.5 0.8 0.8 #Standard deviation *Means in columns followed by the same letters are not significantly different at P <0.05. ¥ Germination/Survival rated on the following scale: 0=poor (<25% germination), 1=fair (30-45%), 2=moderate (50-65%), 3=good (70-85%), 4=excellent (90-100%).

Table 2. Germination and survival evaluations of three milkweed species at the Lockeford Plant Materials Center, CA 2019. Fall Seeded Milkweed - 2019 Germination and Survival Evaluations ꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷGermination/ Survival¥ꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷ Planting Type Planting Date 4/12/2019 4/25/2019 5/17/2019 5/23/2019 6/20/2019 7/16/2019 7/30/2019 8/16/2019 8/29/2019 9/19/2019 Asclepias eriocarpa 11/6/2017 0.0 a 0.5 a 1.0 a 1.0 a 1.3 a 1.3 a 1.3 a 0.5 ab 0.0 b 0.0 b Asclepias fascicularis 11/6/2017 0.0 a 0.5 a 1.0 a 1.5 a 1.8 a 1.5 a 1.5 a 0.0 b 0.0 b 0.0 b Asclepias speciosa 11/6/2017 0.3 a 0.8 a 1.0 a 1.0 a 1.3 a 1.0 a 1.0 a 1.0 a 1.0 a 1.0 a Mean 0.1 0.6 1.0 1.2 1.4 1.3 1.3 0.5 0.3 0.3 # SD 0.3 0.5 0.0 0.4 0.5 0.5 0.5 0.5 0.5 0.5 #Standard deviation *Means in columns followed by the same letters are not significantly different at P <0.05. ¥Germination/Survival rated on the following scale: 0=poor (<25% germination), 1=fair (30-45%), 2=moderate (50-65%), 3=good (70-85%), 4=excellent (90-100%).

Table 3. Height measurements of three milkweed species at the Lockeford Plant Materials Center, CA 2018. Fall Seeded Milkweed - 2018 Height Evaluations ꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷHeight (inches)ꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷ Species Planting Date 5/24/2018 6/18/2017 7/5/2018 7/16/2018 8/15/2018 9/12/2018 Asclepias eriocarpa 11/6/2017 2.6 a 3.5 b 5.8 b 8.3 a 11.8 b 10.4 b Asclepias fascicularis 11/6/2017 3.3 a 7.4 a 12.2 a 14.2 a 20.8 a 26.8 a Asclepias speciosa 11/6/2017 3.3 a 4.4 b 7.3 ab 12.5 a 16.1 ab 15.7 b Mean 3.0 5.1 8.4 11.1 16.2 17.6 # SD 0.6 2.1 3.6 3.5 4.7 7.6 #Standard deviation *Means in columns followed by the same letters are not significantly different at P <0.05.

2018 Height Evaluations for Three Seeded Milkweed Species 30.0 a 25.0

a 20.0

ab b 15.0 a Asclepias eriocarpa a a b Height (in) b Asclepias fascicularis 10.0 a ab a Asclepias speciosa b b 5.0 b a a a 0.0 5/24/2018 6/18/2017 7/5/2018 7/16/2018 8/15/2018 9/12/2018 Date

Figure 4. Height of woollypod milkweed (Asclepias eriocarpa), narrow leaf milkweed (Asclepias fascicularis), and showy milkweed (Asclepious speciosa) in 2018. Columns with the same letters are not significantly different at P<0.05.

Table 4. Height measurements of three milkweed species at the Lockeford Plant Materials Center, CA 2019. Fall Seeded Milkweed - 2019 Height Evaluations ꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷHeight (inches)ꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷ Species Planting Date 4/25/2019 5/23/2019 6/27/2019 7/23/2019 8/23/2019 Asclepias eriocarpa 11/6/2017 5.7 c 9.6 b 20.2 22.8 26.3 b Asclepias fascicularis 11/6/2017 9.0 b 12.0 b 24.8 26.6 15.2 c Asclepias speciosa 11/6/2017 11.9 a 20.4 a 44.8 49.7 51.2 a Mean 8.9 14.0 29.9 33.0 30.9 # SD 3.1 5.3 11.5 12.7 15.9 #Standard deviation *Means in columns followed by the same letters are not significantly different at P <0.05. 2019 Height Evaluations for Three Seeded Milkweed Species 60.0

a 50.0

40.0

30.0 Asclepias eriocarpa b

Height (in) Asclepias fascicularis 20.0 a Asclepias speciosa c a b 10.0 b b c

0.0 4/25/2019 5/23/2019 6/27/2019 7/23/2019 8/23/2019 Date

Figure 5. Height of woollypod milkweed (Asclepias eriocarpa), narrow leaf milkweed (Asclepias fascicularis), and showy milkweed (Asclepious speciosa) in 2019. Columns with the same letters are not significantly different at P<0.05.

Table 5. Disease and insect resistance of three milkweed species at the Lockeford Plant Materials Center, CA 2018. Fall Seeded Milkweed - 2018 Disease and Insect Evaluations Planting ꟷꟷꟷꟷꟷꟷDisease Resistance£ꟷꟷꟷꟷꟷꟷ ꟷꟷꟷꟷꟷꟷInsect Resistance£ꟷꟷꟷꟷꟷꟷ Planting Type Date 8/15/2018 8/30/2018 9/12/2018 8/15/2018 8/30/2018 9/12/2018 Asclepias eriocarpa 11/6/2017 0.0 a 2.5 a 2.8 a 1.8 a 3.3 a¢ 3.3 a¢ Asclepias fascicularis 11/6/2017 0.3 a 2.8 a 2.8 a 2.0 a 3.3 a 3.5 a Asclepias speciosa 11/6/2017 0.0 a 1.5 a 1.3 a 1.5 a 2.4 a 2.3 a Mean 0.1 2.3 2.3 1.8 3.0 3.0 # SD 0.3 1.0 1.1 0.6 0.6 0.9 #Standard deviation *Means in columns followed by the same letters are not significantly different at P <0.05. ¢There were significant differences in ranks between cultivars according to Kruskal-Wallis one-way analysis of variance, but no separation of the ranks was achieved with Dunn’s all pairwise comparison test. £ Disease/Insect Resistance rated on the following scale: 0=no damage, 1=slight damage, 3=moderate damage, 5=severe damage.

Table 6. Disease and insect resistance of three milkweed species at the Lockeford Plant Materials Center, CA 2019. Fall Seeded Milkweed - 2019 Disease and Insect Evaluations Planting ꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷDisease Resistance£ꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷ ꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷInsect Resistance£ꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷꟷ Planting Type Date 6/27/2019 7/16/2019 7/30/2019 8/16/2019 9/19/2019 6/27/2019 7/16/2019 7/30/2019 8/16/2019 9/19/2019 Asclepias eriocarpa 11/6/2017 1.0 ab 2.8 ab 4.0 a 4.5 ab 4.8 a 1.0 ab 3.0 a 3.0 a 3.0 a 3.3 a Asclepias fascicularis 11/6/2017 2.5 a 3.0 a 4.3 a 5.0 a 2.0 b 2.5 a 2.8 a 3.0 a 3.0 a 3.0 a Asclepias speciosa 11/6/2017 0.3 b 0.0 b 1.3 b 2.8 b 3.0 ab 0.3 b 1.0 b 3.0 a 3.0 a 3.0 a Mean 1.3 1.9 3.2 4.1 3.3 1.3 2.3 3.0 3.0 3.1 # SD 1.1 1.5 1.5 1.1 1.2 1.1 1.0 0.0 0.0 0.3 #Standard deviation *Means in columns followed by the same letters are not significantly different at P <0.05. £Disease/Insect Resistance rated on the following scale: 0=no damage, 1=slight damage, 3=moderate damage, 5=severe damage.

Figure 6. Showy milkweed plots, May 2019. Figure 7. Narrow leaf milkweed plots, May 2019

Figure 8. Woollypod milkweed plots, May 2019. Figure 9. A monarch caterpillar hiding in a woollypod milkweed plant. Margaret Smither-Kopperl, Manager; Valerie Bullard, Agronomist, Lockeford Plant Materials Center, 21001 N. Elliott Rd., Lockeford, CA 95237. Jessa Kay Cruz, Senior Pollinator Conservation Specialist Xerces Society, [email protected].

CONCLUSION Evaluations of three seeded milkweed species across two years indicate that establishing these species by seed can be successful. Narrow leaf and woollypod milkweed both establish relatively quickly in the first year, however, survival rates are dramatically reduced if disease and insect pressure are high. Showy milkweed was more successful across plots during the second growing season. Once established, it had higher survival rates and was significantly taller than the other two species. Showy milkweed also had higher insect and disease resistance during both growing seasons. Successfully establishing milkweed from seed can be greatly improved with supplemental irrigation, and intensive weed management during the first year of installation. Early scouting for insect and disease presence is also highly recommended.

Acknowledgements

Special thanks to Hedgerow Farms Winters, CA for their generous donation of all of the plant materials and to Manager, Patrick Reynolds, for assistance and input designing these trials.

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Stevens, M. 2000. Plant Guide for showy milkweed (Asclepias speciosa). USDA-Natural Resources Conservation Service, National Plant Data Center. Tilley, D. 2016. Propagation protocol for production of Container (plug) Asclepias speciosa Torr. Plants 10 cubic inch conetainer; USDA NRCS - Aberdeen Plant Materials Center Aberdeen, Idaho. In: Native Plant Network. URL: http://NativePlantNetwork.org (accessed 2017/04/10). Xerces Society.2020. The Western Monarch Thanksgiving and New Years Day Counts. https://www.westernmonarchcount.org/data/ (accessed on April 1, 2020).

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