Maryland Grows

Basil Bounces Back With Downy Mildew Resistant Cultivars

Basil downy mildew arrived in the U.S. (Florida) in 2007 and has been devastating Italian sweet basil crops in Maryland and other states ever since.

The disease (technically a water mold) can only survive on live basil plants so it does not overwinter outdoors in Maryland. The infection moves from southern states northward each summer.  Infected leaves turn yellow between major veins and this symptom eventually spreads across the leaf.  The characteristic sign of the pathogen appears as a fuzzy grayish-purple coating (sporangia) on the lower leaf surfaces.  Infected leaves eventually turn brown and plants collapse during warm, humid weather.


Spore structures

Spore structures (sporangia) of basil downy mildew on leaf undersides.


Resistance to the Rescue!

Thankfully, breeders have been busy developing resistant cultivars for this popular crop. Over the past two years Rutgers University has released four cultivars, ‘Obsession,’ ‘Devotion,’ ‘Passion,’ and ‘Thunderstruck’. An Israeli breeder developed ‘Prospera’ and Proven Winners came out with ‘Amazel,’ which is seed sterile and propagated from cuttings- so only available as plants.


Trials in Maryland

A limited field evaluation of four basil cultivars- three with reported resistance and one susceptible cultivar- was conducted during the 2019 growing season at three Maryland sites: Westminster, Finksburg, and Ellicott City (Central MD Research & Education Center).

Plants were established in the fourth week of May. Field observations of downy mildew symptoms were noted weekly. Plants were rated on a score of 0 – 10 with zero being free of disease. Disease ratings below were combined from the three sites.

BASIL August 10, 2019 Sept 3, 2019 Oct 7, 2019
‘Amazel’ 0 0 0
‘Prospera’ 0 0 0
‘Devotion’ 0 1 2
‘Obsession’ 0 1 2
‘Aroma’ (susceptible cultivar) 5 9 10
Basil cultivars

Basil cultivars left to right ‘Amazel’, ‘Aroma,’ and ‘Prospera’ (8/15/19)



Basil cultivar ‘Obsession” with mild downy mildew symptoms (9/5/2019)


Disease symptoms were first noted on August 10 on ‘Aroma,’ and progressed rapidly.  Observations of the resistant cultivars continued through October 8.  By September 3rd, downy mildew had caused very faint yellowing on the lower leaves of ‘Devotion’ and ‘Obsession’. In general, all the resistant basil cultivars performed quite well compared to the susceptible cultivar ‘Aroma’.  Mild disease symptoms on the Rutgers cultivars ‘Devotion’ and ‘Obsession’ did not progress; plant damage was very minor. Prospera’ and ‘Amazel’ never developed disease symptoms during the trial.


HGIC also received positive reports from UME Master Gardeners and other gardeners about the productivity and resistance to downy mildew of ‘Prospera,’ ‘Obsession,’ and ‘Devotion’.


Seed Availability

‘Devotion,’ ‘Obsession,’ and ‘Prospera’ seeds are sold by Johnny’s Seeds and High Mowing Seeds. Harris Seeds is carrying ‘Prospera’ seeds.


Other resistant cultivars: ‘Pesto Party’ has shown limited suppression of basil downy mildew (seeds available from Burpee Seeds). Be on the look-out in 2021 for the other new cultivars from the Rutgers breeding program, ‘Thunderstruck’ and ‘Passion,’ that show very good resistance to downy mildew.




By Jon Traunfeld and Dave Clement, Ph.D., Extension Specialists, UME

How to Easily Seed Start Onions and Leeks – Featured Video

You can start onions and leeks 8-12 weeks indoors before you plant them outside.  Take a look at this seed starting method.

Learn more about seed starting on the HGIC website.


The Garden Hoes Podcast – 04 – Garden Tool Care

Garden Hoes Podcast

Great news! We are now available on both iTunes and Stitcher, making it easy for you to listen to The Garden Hoes Podcast on the go!

  • In this episode, we talk about environmentally friendly de-icers, understanding seed catalogs and packets (~6:18), and tool care (~11:37). 
  • Garden Tip of the Month: House plants and starting seeds inside (~19:15) 
  • Bug of the Month: Mealybugs (~23:25)
  • Native Plant of the Month: Skunk cabbage ( ~27:37)

For more information about University of Maryland Extension and these topics, please check out the Home and Garden Information Center website at

If you have a garden question or topic you would like us to talk about you can email us at

Listen to the podcast.

Plant Love & Compatibility: A Valentine’s Tribute to Pollination

February is Valentine’s month, but also that of starting to feel impatient about gardening and all the yummy veggies and fruits that will come through the season. Those two things (Valentine’s, and fruits and veggies) are actually really connected, and in today’s post, we will dive into how that is so. 

Valentine’s and fruits and veggies are connected? I don’t get it…

Have you asked yourself how those fruits you see are formed? In fact, this has a lot to do with love (well, plant love) and partner compatibility… quite a bit like Valentine’s couples! Like humans, plants have special organs they use to reproduce, which are all in the flowers (Figure 1).

flower parts

Figure 1. A flower has all the plant’s reproductive organs.

When plants reproduce, their offspring are their seeds. Until here all is nice and good, however, a plant’s problem is that because it can’t move, if all the seeds it produces were to just to fall right under it, the mother plant would soon be surrounded by her offspring, which would then compete with each other and herself. To deal with this problem, and because plants are cool, they have evolved some super-smart strategies to help their seeds be dispersed: fruits! (Figure 2)

beans and apples

Figure 2. Fruits allow plants to disperse their seeds. Some fruits can be fleshy like in apples, or dry like in almonds, while some are able to explode and propel the seeds into the air like in beans.

In wild plants (and many cultivated ones), the fruit is the packet that will carry or disperse the seeds, and among all fruits, the fleshy ones are actually a ‘bait’ for seed dispersers. In fact, these fleshy parts are usually sweet and nutritious, and thus attract animals that eat this ‘seed packet’ (often along with the seeds). However, because an animal digestive system is built the way it is, eating the fruit will usually also mean dispersing the seeds in a different place, when those seeds leave the animal’s body. So, you see, plants having offspring and fruits are directly related, like Valentine’s and my veggies and fruits!

Oooh… so, plants can only make fruit if there has been pollination?

Making a fruit requires a lot of energy from the plant (think about all those sugars and colors that go into that delicious tomato!). This means that it usually is the case that fruits will only form if pollination has happened and seeds have formed. So, if one wants a garden to produce fruits and vegetables, it is very likely that pollination and seed formation will need to happen for it to be productive.

Plants produce seeds and are pollinated in many different ways (see this blog post for examples), but it is pretty common that plants will produce more seeds and larger fruits if they receive pollen from a plant individual that is distantly-related. In fact, as for many animals, crossing among too closely-related individuals can lead to genetic diseases and poor health. And this is why pollinators are so important; they allow pollen from different individuals to be transferred among plants of the same species and allow for healthy seeds.

Is this why I sometimes need many similar plants to produce fruit?

Yes! Many groups of plants have developed reproductive strategies that advantage fertilization by pollen from plants that are more distantly-related over those from themselves or a very closely-related individual. We say that these plants need cross-pollination for producing seeds (and fruit).

On the other hand, there are some plants that are able to make fruits while receiving pollen from themselves or from closely-related individuals. Because these plants are equally exposed to the health problems associated with producing seeds with a closely-related individual, they have developed other strategies that can help them reduce the occurrence of such an event; for example, their seeds can disperse very long distances.

What are the plants that need cross-pollination?

Apples, pears, almonds, pistachio, some cherries, apricots, figs, and paw-paws are all plants that need to receive pollen from another plant of the same species to make fruits. Further, note that for many of these plants it is not just sufficient to have another plant of the same species; this plant has to be of a different variety and has to be present at a relatively short distance.

Unlike those mentioned above, tomatoes, bell peppers, eggplants, grapes, currants, raspberries, and gooseberries can self-pollinate, and thus do not require other surrounding plants of the same species to produce fruits.

Many plants are able to produce fruit by self-pollinating but are far more productive if they are cultivated along with other plants of the same species. This is the case of blueberries, huckleberries, and persimmon.

Finally, some plants, like kiwi, have male and female flowers on different individuals. In these species, although the only fruit-bearing individuals are the female plants, the fruit will only form if a male is present close by.

To help disperse their seeds, some plants have evolved pretty extreme strategies. Take a look at this video to learn more about some of them!

By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park. See more posts by Anahí.

Fastest vegetable gardening ever! (A.k.a. microgreens.)


Have you tried those very expensive packages of cute little nutritionally-packed microgreens to sprinkle on top of your meals? Did you think, well, this adds something fun and tasty to dinner, but how often am I going to shell out that amount of money? Occasionally, maybe (microgreens provide a great income source for farmers in the wintertime), but if you’re hooked and you want to eat these tiny bursts of flavor more often, grow your own! Read More

February Tips and Tasks

Houseplants by window

  • Day length is increasing and the sunlight is more intense. Houseplants will begin to show signs of new growth. It is time to start fertilizing your indoor plants.
  • Leaf yellowing and leaf drop from houseplants can be a result of low light conditions combined with overwatering. Spider mites are another possible cause.
  • Spring bulbs can still be planted if the ground is not frozen. Inspect the bulbs and plant only the solid, healthy ones as bulbs can deteriorate when stored.  They may still bloom this year but will not be as vigorous. Do not cut back the green foliage that emerges, let it die back naturally.
  • Keep garden beds covered with shredded leaves, straw, or bark mulch to minimize the risk of soil erosion and nutrient run-off.
  • The Maryland Lawn Fertilizer Law prohibits anyone from using fertilizer products to melt ice and snow on steps, sidewalks or driveways.

Find more February Tips and Tasks on the HGIC website.

Helen’s Flower Hails Pollinators

common sneezeweed flowers

Helenium autumnale. Photo: Beverly Turner, Jackson Minnesota,

Helen’s flower is an underdog when it comes to native plants. It is not as well known or as popular as butterfly milkweed, bee balm, or black-eyed Susans — but perhaps it’s time for its day in the sun. It makes a nice addition to a pollinator garden.

Helenium autumnale is the species name of this North American native perennial plant. It goes by the (somewhat unfortunate) name of “common sneezeweed” because dried parts of the plant were formerly used for making snuff to induce sneezing. As an ornamental garden plant, it is not known to prompt sneezes from pollen dispersal (it relies on insects for pollination) and I prefer to address it by its lovelier common name, Helen’s flower… or just plain Helenium.

Wild Helenium autumnale boasts cheerful yellow button-like flowers tended by a skirt of turned-down petals in late summer to fall. Its natural habitat in Maryland includes swamps and moist riverbanks, so in your garden, it will like a location where it has some regular soil moisture. It can grow in full sun or partial shade and stretches in height from 2 to 5 feet tall. The flowers support a variety of pollinators such as bees, wasps, syrphid flies, butterflies, and beetles.

A wide variety of cultivars of Helenium are now available. They range in color from bright canary yellow to orange and crimson and various combinations in between. Many of the cultivars tolerate drier soil and have a more compact habit.

Mt. Cuba Center in Delaware conducted field trials of 44 Helenium species and cultivars from 2017 to 2019. They evaluated plants for their habit, vigor, disease resistance, floral display, and pollinator visits.

helenium flowers in a garde

Helenium flowers in a garden, “The warm glow of early Autumn” by hehaden, Flickr

Given the high interest in pollinator gardens right now, I was curious about their observations of pollinator visits in particular.

The native Helenium autumnale had the most observed pollinator visits (162), while the cultivar H. ‘Zimbelstern’ came in second (151). Both of these had excellent powdery mildew resistance as well. Other cultivars such as Helenium autumnale ‘Can Can’ and H. ‘Tijuana Brass’ also had excellent ratings for these two characteristics. The best performers in the study overall (considering all the characteristics evaluated) were ‘Kanaria’, ‘Zimbelstern’, and ‘Can Can.’

The native Helenium autumnale had the most observed pollinator visits (162), while the cultivar H. ‘Zimbelstern’ came in second (151).

For all the details and results of the evaluation, read the report online.  

If you plan to start (or add to) a pollinator garden this spring, do consider adding Helen’s flower if you have a moist site in full sun or partial shade. Mt. Cuba’s report provides good information on plant care, including staking and pruning tips and recommendations for managing the two most common diseases — powdery mildew and aster yellows.

To purchase plants, check the Maryland Native Plant Society’s website for spring native plant sales and nursery sources.

Visit the Home & Garden Information Center website for additional resources on native plants and gardening for pollinators.

By Christa K. Carignan, Coordinator, Digital Horticulture Education, University of Maryland Extension Home & Garden Information Center. Read additional posts by Christa.